Electrical Objective Book

2013-14

ELECTRICAL OBJECTIVE QUESTION

MADE BY:-

P.M.MEVADA

P.M.MEVADA

TABLE OF CONTENTS SUBJECT CHAPTER-1. BASIC ELECTRICAL ENGINEERING CHAPTER-2. ELECTRICAL MACHINE 2.1 – ALTERNATOR 2.2 – D.C. MACHINES 2.3 – D.C. MOTOR 2.4 - INDUCTION MOTORS 2.5 – SYNCHRONOUS MOTOR 2.6 – GENERAL ELECTRICAL MACHINE CHAPTER-3. TRANSFORMERS CHAPTER-4. POWER SYSTEM CHAPTER-5. POWER ELECTRONICS CHAPTER-6. OP-AMP CHAPTER-7. MEASUREMENTS & INSTRUMENTATION CHAPTER-8. BASIC ELECTRONICS CHAPTER-9. CONTROL SYSTEM CHAPTER-10. ELECTRICAL CIRCUIT THEORY

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ELECTRICAL INTERVIEW QUESTION & ANSWER

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CHAPTER -1. BASIC ELECTRICAL ENGINEERING [1] Which of the following can vary with ac, but never with dc? A. Power B. Voltage C. Frequency D. Amplitude [2] If all other factors are kept constant, the inductance of the air-core coil is not affected by A. The frequency B. The number of turns C. The diameter of the coil D. The length of the coil [3] The length of time between a point in one cycle and the same point in the next cycle of an ac wave is the A. Frequency B. Magnitude C. Period D. Polarity [4] Capacitance acts to store electrical energy as A. Current B. Voltage C. A magnetic field D. An electric field [5] On a spectrum analyzer, a ac signal having only one frequency component looks like A. A single pip B. A sine wave C. A square wave D. A sawtooth wave [6] A ferromagnetic core is place in the inductor to A. Increase the current carrying capacity B. Increase the inductance C. Limit the current D. Reduce the inductance [7] The period of a ac wave, in seconds is A. The same as the frequency in hertz B. Not related to the frequency in any way C. Equal to 1 divided by the frequency in hertz D. Equal to the peak amplitude in volts divided by the frequency in hertz [8] An inductor works by A. Charging a piece of wire B. Storing energy as a magnetic field C. Choking off dc D. Introducing resistance into a field [9] As capacitor plate area increases A. The capacitance increases B. The capacitance decreases C. The capacitance does not change D. The current handling ability decreases [10] In a small inductance A. Energy is stored and released slowly B. The current flow is always large C. The current flow is always slow D. Energy is stored and released quickly [11] In ac circuit, the ratio of kW/kVA is A. power factor B. form factor


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P.M.MEVADA C. load factor D. diversity factor [12] Suppose that two ac waves have the same frequency but differ in phase by exactly 1/20 of a cycle. What is the phase difference between these two waves? A. 18 deg B. 20 deg C. 36 deg D. 5.73 deg [13] The unit of inductance is A. Mho B. hendry C. ohm D. farad [14] What is the angular frequency of the ac signal having a frequency of 1770Hz A. 1770 rad/s B. 11,120 rad/s C. 282 rad/s D. Data insufficient [15] Thevenin's equivalent circuit consists of A. series combination of Rth, Eth, Rl B. series combination of Rth, Eth C. parallel combination of Rth, Eth, Rl D. parallel combination of Rth, Eth [16] The frequency of DC supply is A. 16 2/3 Hz B. 60 Hz C. 50 Hz D. 0 Hz [17] Load factor is defined as the ratio of A. max demand/ average demand B. average demand/ connected load C. average demand/ max. demand D. connected load/ max demand [18] Q factor of an inductive coil is given by A. 2π fL/R B. 2π fr/R C. R/Z D. lr/l [19] The rms value of sinusoidal 100V peak to peak is A. 100 V B. 50/√2 V C. 50 V D. 100/√2 V [20] Which of the following bulbs will have the least resistance? A. 220V, 60W B. 220V, 100W C. 115V, 60W D. 115V, 100W [21] The wire is stretched to double its length, then its resistance R will become A. r/2 B. 4r C. 2r D. r/4


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P.M.MEVADA [22] The power drawn by the circuit whose input is 20KVA and p.f is 0.8 lagging A. 12 B. 20 C. 16 D. 8 [23] The combined resistance of two equal resistors connected in parallel is equal to A. One half the resistance of one resistor B. twice the resistance of one resistor C. four times the resistance of one resistor D. one fourth the resistance of one resistor [24] The superposition theorem is applicable to circuits only having ............ elements A. non-linear B. passive C. resistive D. linear bilateral [25] The Q-factor of a coil is given by A. its power factor B. Ratio of max. energy stored & energy dissipated per cycle. C. reciprocal of its power factor D. ratio R/Z [26] The power factor at resonance in RLC circuit is A. zero B. unity C. 0.5 lagging D. 0.5 leading [27] Cells are connected in parallel to A. Increase the available voltage B. Reduce the cost of wiring C. Increase the available current D. Reduce the time required to fully charge them after use [28] the power factor of a purely resistive circuit is A. zero B. unity C. lagging D. leading [29] Which of the following has minimum running cost? A. Hydro electric station B. nuclear power station C. thermal power station D.diesel power station [30] The color code of a resistor 2.7Kohm with the tolerance of 10% is A. red, violet, red and silver B. red, violet, yellow and gold C. red, violet, orange, silver D. red, violet, red,gold [31] In a 117Vrms utility circuit, the peak-to-peak voltage is approximately A. 82.7 V B. 165 V C. 234 V D. 331 V [32] Watt hour is the unit of A. Electric power B. Electric capacity C. Electric energy D. Electric charge


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P.M.MEVADA [33] In India,electrical power is transmitted by A. 1-phase ac system B. 3-wire dc system C. 3-phase 3-wire ac system D. 2 wire dc system [34] If two perfect sine waves have the same frequency and the same phase, the composite wave A. Is a sine wave with an amplitude equal to the difference between the amplitude of the waves B. Is a sine wave with an amplitude equal to the sum of the amplitudes of the two original waves C. Is not a sine wave, but has the same frequency as the two input waves D. Has zero amplitude (ie, it does not exist) because the two input waves cancel each other out. [35] In a ac circuit the product of voltage and current is known as A. Power B. Real Power C. Resistive power D. Apparent power [36] The advantage of AC over DC in utility applications is A. AC is easier to transform from one voltage to another B. AC is transmitted with lower loss in wires C. AC can be easily obtained from dc generators D. AC can be generated with less dangerous by products [37] A network that does not have either voltage or current source is called ......network A. Active B. Passive C. Resistive D. Dummy [38] The sixth harmonic of a ac wave whose period is 1 Milli second has a frequency of A. 0.006Hz B. 167.0 Hz C. 7.0 kHz D. 6 kHz [39] A degree of phase represents A. 6.28 cycles B. 57.3 cycles C. 1/60 of a cycle D. 1/360 of a cycle [40] A battery is source of A. DC voltage B. 1 phase AC voltage C. 3 phase ac voltage D. ac or dc voltage [41] The power plant having highest efficiency is A. Hydro B. Thermal C. Nuclear D. Diesel [42] As the spacing between plates in a capacitor is made smaller A. The capacitance increases B. The capacitance decreases C. The capacitance does not change D. The resistance increases [43] The relationship between frequency and time period of ac waveform is A. f = T B. f = 1/ T2


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P.M.MEVADA C. f = 1/T D. f = T2 [44] The five 0.050uF capacitors are connected in parallel. The equivalent capacitance is A. 0.010 uf B. 0.25 uf C. 0.50uf D. 0.025uf [45] The current gain of a bipolar transistor drops at high frequencies because of A. Transistor capacitance B. High current effects in the base C. Parasitic inductive elements D. the early effect [46] If two perfect sine waves have the same frequency and the same amplitude, but are in opposite phase, the composite wave A. Has twice the amplitude of either input wave alone B. Has half the amplitude of either input wave alone C. Is complex, but has the same frequency as the originals. D. Has zero amplitude ( that is, it does not exist) because the two input waves cancel each other out. [47] Three capacitors are connected in series having capacitance of 8uF, 32uF, 16uF, the total capacitance is A. 32/7 uF B. 7.32 uF C. 56 uF D. 32 uF [48] Which one of the following does not affect the power output available from a particular ac generator? A. The strength of the magnet B. The number of turns in the coil C. The type of natural energy source used D. The speed of rotation of the coil or magnet [49] Which of the following are active components A. resistor and inductor B. Diode, BJT, FET C. Opamp, BJT, thermionic triode D. Capacitor, Inductor [50] The energy required to charge a 10 uF capacitor to 100V is (a) 0.10 J (b) 0.05 J (c) 5 X 10-9 J (d) 10 X 10-9 J [51] The current in a inductor changes from 0 to 200mA in 4ms and induces a voltage of 100mV. The value of inductor is (a) 2mH (b) 0.5mH (c) 8mH (d) 4mH [52] A battery has a short-circuit current of 30A and an open circuit voltage of 24V. If the battery is connected to an electric bulb of resistance 2 ?, the power dissipated by the bulb is (a) 80W (b) 1800W (c) 112.5W (d) 228W [53] Which of the following is ferromagnetic material? a) Copper b) Palladium c) Silver


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P.M.MEVADA d) Cobalt [54] A complex wave form made up frequency components 1 Hz, 3 Hz, 5 Hz, 7 Hz and 9 Hz. Its fundamental frequency is a) 9 Hz b) 12.5 Hz c) 1 Hz d) Indeterminate [55] If a 175V dc source were connected in series with the utility mains from a standard wall outlet, the result would be A. Smooth dc at a constant voltage B. Pure ac with equal peak voltages C. Ac with one peak voltage greater than the other D. Fluctuating dc [56] The main advantage of air as a dielectric material for capacitors is A. Has a high dielectric constant B. Is not physically dense C. Has low loss D. Allows for large capacitance in a small volume [57] Which of the following is a polarized capacitor? A. Paper B. Mica C. Inter electrode D. Electrolytic [58] In a 117Vrms utility circuit, the positive peak voltage is approximately A. 82.7V B. 165V C. 234V D. 331V [59] If a capacitor has a negative temperature coefficient then A. Its capacitance decreases as the temperature rises B. Its capacitance increases as the temperature rises C. Its capacitance does not change with temperature D. It will not work if the temperature is below freezing [60] Inductors in series, assuming there is no mutual inductance, combine A. Like resistors in parallel B. Like resistors in series C. Like batteries in series with opposite polarities D. In a way unlike any other type of component [61] The five 0.050 μF capacitors are connected in series. The equivalent capacitance is A. 0.010 μf B. 0.25 μf C. 0.50 μf D. 0.025 μf [62] A material with a high dielectric constant A. Acts to increase capacitance per unit volume B. Acts to decrease capacitance per unit volume C. Has no effect on capacitance D. Causes a capacitor to become polarized [63] In a perfect sine wave, the peak to peak amplitude is equal to A. Half the peak amplitude B. The peak amplitude C. 1.414 times the peak amplitude D. Twice the peak amplitude [64] A triangular wave exhibits A. An instantaneous rise and a defined decay


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P.M.MEVADA B. A defined rise and an instantaneous decay C. A defined rise and a defined decay, and the two are equal D. An instantaneous rise and an instantaneous decay [65] The colour bands on a carbon composition resistor occur in the sequence: yellow, violet, yellow and silver. Its resistance is (a) 470 KΩ± 47 KΩ (b) 470 KΩ± 23.5 % (c) 47 KΩ± 10 % (d) 47 KΩ± 5 % [66] If 120°C of charge passes through an electric conductor in 60 sec, the current in the conductor is (a) 0.5A (b) 2A (c) 3.33mA (d) 0.3mA [67] The energy required to move 120 coulomb through 3V is (a) 25mJ (b) 360J (c) 40J (d) 2.78mJ [68] The current carrying capacity of a 1W, 4MΩ resistor used in radio receiver is (a) 0.5kA (b) 2kA (c) 2mA (d) 0.5mA [69] A capacitor is charged by a constant current of 2mA and results in a voltage increase of 12V in a 10 sec interval. The value of capacitance is (a) 0.75mF (b) 1.33mF (c) 0.6mF (d) 1.67mF [70] Three phase ac supply A. Has sawtooth waves that add together in phase B. Consists of three sine waves in different phases C. Is a sine wave with exactly three harmonics D. Is of interest only to physicists [71] Power is defined as A. the rate at which current flows in a circuit B. the product of voltage and resistance in a circuit C. the rate at which energy is radiated or dissipated D. the accumulation of energy over time E. the amount of heat generated in a circuit. [72] At the exact moment a 60Hz ac sine wave is at its positive peak voltage, the instantaneous rate of change in the voltage is A. Large and positive B. Small and negative C. Large and negative D. Small and negative E. Zero [73] A flute sounds different than a violin, even if the two instruments are played at the same pitch, because of a difference in the A. Phase B. Chamber length C. Frequency D. Waveform E. Bias


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P.M.MEVADA [74] A common-collector transistor circuit is often used A. to provide high gain and sensitivity over a wide range of frequencies B. to match a high impedance to a low impedance C. as a high-fidelity audio power amplifier D. as an oscillator at microwaves frequencies E. as the rectifier in a dc power supply. [75] The internal conductance of an ammeter is generally A. Low B. Directly proportional to the current C. Inversely proportional to the current D. High E. Any value. It doest matter [76] A steady magnetic field can be produced by A. a straight wire carrying a constant direct current. B. a loop of wire carrying a constant direct current. C. a coil of wire carrying a constant direct current. D. a constant-intensity stream of protons in free space, moving in a straight line. E. any of the above. [77] The output wave of a common-gate amplifier circuit with a pure sine-wave input A. is in phase with the input wave. B. lags the input wave by 90° of phase. C. leads the input wave by 90° of phase. D. is 180° out of phase with the input wave. E. is inverted with respect to the input wave. [78] Which of the following capacitor types is polarized? A. Electrolytic B. Paper C. Ceramic D. Mica E. Air variable [79] when a non zero net reactance exists in an ac circuit, the apparent power is A. Zero B. Equal to the true power C. Less than the true power D. Greater than the true power E. Infinite [80] The gauss is a unit of (a) Charge carrier flow speed. (b) Magnetic flux density. (c) Electrostatic field strength. (d) Electromagnetic field intensity. (e) Electrical charge quantity. Ans:B. Exp: In SI system the unit is tesla(T). In CGS system the unit is Gauss [81] An average responding rectifier type electronic ac voltmeter has its scale calibrated in terms of the rms value of a sine wave, when a square wave voltage of peak magnitude 100V is measured using this voltmeter then the reading indicated by the meter, will be ? a) 111V b) 100V c) 90.09V d) 70.7V [82] A house served by a 220V supply light, is protected by a 9-Ampere fuse. The maximum number of 60 W bulbs in parallel that can be turned on is a) 11 b) 33


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P.M.MEVADA c) 22 d) 44 [83] Silicon has a preference in IC technology because (a) it is an indirect semiconductor (b) it is a covalent semiconductor (c) it is an elemental semiconductor (d) of the availability of nature oxide SiO [84] Three equal resistance of magnitude 5 Ohm each are connected in delta. The resistance between any two pair of terminals of the delta will be (a) 5 Ohm (b) 5/3 Ohm (c) 10/3 Ohm (d) 3/5 Ohm [85] The R.M.S. value of a half wave rectified sinusoidal alternating current with peak value Im is (a) Im / 1 (b) Im / v2 (c) Im / 2 (d) Im v3 [86] The unit which indicates the rate at which energy is expended? A. Watt B. Ampere-hour C. Coulomb D. Volt [87] The peak voltage in an ac wave is always A. greater than the average voltage B. less than the average voltage C. greater than or equal to average voltage D. less than or equal to the average voltage [88] When an electrical charge exists but there is no flow of current, the charge is said to be A. ionizing B. electronic C. Static D. Atomic [89] As the number of turns in a coil that carries ac increases without limit, the current in the coil will A. Eventually become very large B. Stay the same C. Decrease, approaching zero D. Be stored in the core material [90] As the number of turns in a coil increases, the reactance at a constant frequency A. Increases B. Decreases C. Stays the same D. Is stored in the core material [91] In an RL circuit, as the ratio of inductive reactance to resistance (XL/R) decreases, the phase angle A. Increases B. Decreases C. Stays the same D. Becomes alternately positive and negative [92] The best filter for a power supply is A. a capacitor in series B. a choke in series C. a capacitor in series and a choke in parallel D. a capacitor in parallel and a choke in series


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P.M.MEVADA [93] Voltage regulation can be achieved by a zener diode connected in A. parallel with the filter output, forward biased B. parallel with the filter output, reverse biased C. series with the filter output, forward biased D. series with the filter output, reverse biased [94] A current surge takes place when a power supply is first turned on because A. the transformer core is suddenly magnetized B. the diodes suddenly start to conduct C. the filter capacitor must be initially charged D. arching takes place in the power switch [95] A dc electromagnet A. has constant polarity B. Requires an air core C. Cannot be used to permanently magnetize anything D. Does not attract or repel permanent magnet [96] In a multi-stage RC coupled amplifier the coupling capacitor______________ A) Limits the low frequency response B) Limits the high frequency response C) Does not affect the frequency response D) Block the DC component without affecting the frequency response [97] It is required to measure temperature in the range of 13000 deg C to 15000 deg c. The most suitable thermocouple to be used as a transducer would be? a) chromel - constantan b) Iron - constantan c) chromel - alumel d) platinum- rhodium [98] Telemetering is a method of? a) Counting pulses sent over long distances b) Transmitting pictures from one place to another c) Transmitting information concerning a process over a distance d) None [99] A dc to dc converter having an efficiency of 80% is delivering 16W to a load. If the converter is generating an output of 200V from an input source of 20V, then the current drawn from the source will be? a) 0.1A b) 0.5A c) 1.0A d) 10.0A [100] The location of lighting arrestor is? a) Near the transformer b) Near the circuit breaker c) Away from the transformer d) None [101] Which of the following is not a general characteristic of ac wave? A. The wave shape is identical for each cycle B. The polarity reverses periodically C. The electrons always flow in the same direction D. There is a definite frequency [102] All sine waves A. Have similar general appearance B. Have instantaneous rise and fall times C. Are in the same phase as cosine waves D. Rise instantly, but decay slowly [103] The derivative of a sine wave A. Is shifted in phase by ½ cycle from the sine wave B. Is the rate of change in the instantaneous value


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P.M.MEVADA C. Has instantaneous rise and decay times D. Rise instantly, but decays slowly [104] A phase difference of 180deg in the circular motion model of a sine wave represents A. ¼ revolution B. ½ revolution C. A full revolution D. Two full revolution [105] We can add or subtract a ….degrees of phase to or from a wave, and end up with exactly the same wave again A. 90 B. 180 C. 270 D. 360 [106] A wave has a frequency of 300kHz. One complete cycle takes…..seconds A. 1.3000 B. 0.00333 C. 1/3000 D. 3.33 X 10-6 [107] A wave has a frequency of 440Hz, how long does it take for 10: of a cycle to occur? A. 0.00273s B. 0.0000273s C. 0.0000631s D. 0.00000631s [108] One waveform has a peak value of ±3V and the other has peak value of ±5V. These two waves are in phase coincidence. The resultant has voltages of A. ±8Vpk, in phase with the composites B. ±2 Vpk, in phase with the composites C. ±8Vpk, in phase opposition with respect to the composites D. ±2 Vpk, in phase opposition with respect to the composites [109] Two pure sine waves that differ in phase by 180: can be considered to A. Be offset by two full cycles B. Be in phase opposition C. Be separated by less than ¼ cycle D. Have a frequency of ½ cycle [110] A BJT has A. three PN junctions B. three semiconductor layers C. two N type layers around a P type layer D. a low avalanche voltage [111]Consider the following statements: [IES2010] Piezoelectric materials serve as 1.A source of ultrasonic waves 2.When electric field is applied, the mechanical dimensions of the substances are not at all altered. 3.Converts electrical energy to mechanical and vice versa 4.Converts thermal energy to electrical energy Which of the above statements is/are correct? A.1 only B.2 and 3 only C.1 and 3 only D.1,2,3 and 4 [112]The current through the 2KΩ resistance in the circuit shown is [GATE2009]


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P.M.MEVADA

A.0 mA B.1 mA C.2 mA D.6 mA [113]Out of the following plant categories 1.Nuclear 2.Run-of-river 3.Pump storage 4.Diesel the base load power plants are [GATE2009] A.1 and 2 B. 2 and 3 C.1,2 and 4 D.1, 3,and 4 [114]The following circuit has a source voltage Vs as shown in the graph. The current through the circuit is also shown

The element connected between a and b could be [GATE 2009]

[115]The following circuit has R= 10kΩ , C=10μF. The input voltage is a sinusoid at 50Hz with an rms value of 10V. Under ideal conditions, the current is from the source is [GATE 2009]


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A. B. C. D.

10π mA leading by 90° 20π mA leading by 90° 10π mA leading by 90° 10πmA lagging by 90°

Ans: A [116]In the figure shown, all elements used are ideal. For time t<0, S1 remained closed and S2 open. At t=0, S1 is opened and S2 is closed. If the voltage Vc2 across the capacitor C2 at t=0 is zero, the voltage across the capacitor combination at t=0+ will be [GATE 2009]

A. 1V B. 2V C. 1.5V D. 3 V Ans: D [117]Transformer and emitter follower can both be used for impedance matching at the output of an audio amplifier. The basic relationship between the input power Pin and output power Pout in both the cases is [GATE 2009] A. Pin = Pout for both transformer and emitter follower B. Pin > Pout for both transformer and emitter follower C. Pin < Pout for transformer and Pin = Pout for emitter follower D. Pin = Pout for transformer and Pin < Pout for emitter follower Ans: None of the above [118]The equivalent capacitance of the input loop of the circuit shown is [GATE 2009]

A. B. C. D.

2μF 100μF 200μF 4μF


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CHAPTER-2. ELECTRICAL MACHINE 2.1 - ALTERNATOR

[1] Squirrel cage bars placed in the rotor pole faces of an alternator help reduce hunting A. above synchronous speed only B. below synchronous speed only C. above and blow synchronous speeds both D. none of the above [2] The stationary alternator should not be connected to live bus-bars because it A. is likely to run as synchronous motor B. will get short - circuited C. will decrease bus - bar voltage though momentarily D. will disturb generated emf's of other alternators connected in parallel. [3] With a unity load p.f, the effect of armature reaction on the main field flux of an alternator is A. distortional B. magnetising C. demagnetising D. nominal [4] At lagging loads, armature reaction in an alternator is A. cross-magnetising B. demagnetising C. non-effective D. magnetising [5] The frequency of voltage generated by an alternator having 4 poles and rotating at 1800 rpm is A. 60 Hz B. 7200 Hz C. 120 Hz D. 450 Hz [6] The main disadvantages of using short pitch winding in alternators is that it A. reduces harmonics in the generated voltage B. reduces the total voltage around the armature coils C. produces asymmetry in the three phase windings D. increases Cu of end connections. [7] Zero power factor method of an alternator is used to find its A. efficiency B. voltage regulation C. armature resistance D. synchronous impedance [8] Armature reaction in an alternator mainly affects A. rotor speed B. terminal voltage per phase C. frequency of armature current D. generated voltage per phase [9]The effect of increasing air gap length in the induction motor will increase the A. power factor B. speed C. magnetising current D. air gap flux [10] The principle of operation of a 3 phase induction motor is most similar to that of a A. synchronous motor B. repulsion start induction motor C. transformer with a shorted secondary D. capacitor start, induction run motor


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2.2 – D.C. MACHINES [1] Voltage equation of a dc motor is A. V = Eb + IaRa B. Eb = V + IaRa C. V = Eb/IaRa D. V = Eb + Ia2Ra [2] Both Hopkinson's test and Field test A. Require two electrically coupled series motors B. Need two similar mechanically coupled motors C. Use negligible power D. Are regenerative tests [3] which of the following motor has the constant speed? A. Series motor B. Shunt motor C. Cumulatively compound motor D. All of the above [4] The usual test to find the efficiency of the traction motor is A. Field's test B. Retardation test C. Hopkinson's test D. Swinburn's test [5] A DC series motor is best for driving A. Lathes B. Cranes and hoists C. Shears and punches D. Machine tools [6] Retardation test on a dc shunt motor is used for finding A. Stray loss B. Copper loss C. Friction loss D. Iron loss [7] In a DC series motor increasing the load current will A. Decrease the speed B. Increase the speed C. Better commutation D. Increase the back emf [8] One of the main advantage of the swinburn's test is A. It is applicable both shunt and compound motors B. It needs one running test C. It is very economical and convenient D. It ignores any charge in iron loss [9] the main disadvantage of hopkinson's test for finding efficiency of shunt dc motors is that it A. Requires full load power B. Ignores any change in iron loss C. Needs one motor and one generator D. Requires two identical shunt machines [10] The most economical method of finding no losses of a large dc shunt motor is A. Hopkinson's test B. Swinburn's test C. Retardation test D. Field's test


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2.3 – D.C. MOTOR [1] The basic requirement of a dc armature winding is that it must be A. a closed one B. a lap winding C. a wave winding D. either b or c [2] The sole purpose of a commutator in a dc generator is to A. increase output voltage B. reduce sparking at brushes C. provide smoother output D. convert the induced ac into dc [3] In small DC machines, armature slots are sometimes not made axial but are skewed, results in A. quieter operation B. slight decrease in losses C. saving of copper D. both a and b [4] The critical resistance of the dc generator is the resistance of A. armature B. field C. load D. brushes [5] In a dc generator, the generator, the generated emf is directly proportional to the A. field current B. pole flux C. number of armature parallel paths D. number of dummy coils [6] The commutation process in a dc generator basically involves A. passage of current from moving armature to a stationary load B. reversal of current in an armature coil as it crosses MNA C. conversion of ac to dc D. suppression of reactance voltage [7] The essential condition for stable parallel operation of two dc generators having similar characteristics is that they should have A. same kilowatt output ratings B. dropping voltage characteristics C. same percentage regulation D. same no load and full load speed [8] An ideal dc generator has .......... voltage regulation. A. low B. zero C. positive D. negative [9] Which generator has poorest voltage regulation A. series B. shunt C. compound D. high [10] The voltage regulation of an over compound dc generator is always A. Positive B. negative C. zero D. high


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2.4 - INDUCTION MOTORS [1] The crawling in an induction motor is caused by A. improper design of the machine B. low voltage supply C. high loads D. harmonics developed in the motor Ans = D [2] The speed of an induction motor A. decreases too much with the increase of load B. increase with the increase of load C. decreases slightly with the increase of load D. remains constant with the increase of load [3] The effect of increasing the length of the air gap in an induction motor will increase A. power factor B. speed C. magnetising current D. air-gap flux [4] the difference between the synchronous speed and the actual speed of an induction motor is known as A. Regulation B. back lash C. slip D. lag [5] Rotating magnetic field is produced in A.... A. single - phase induction motor B. three phase induction motor C. dc series motor D. ac series motor [6] The stator core of the induction motor is made of A. Laminated cast iron B. Mild steel C. Silicon steel stampings D. Soft wood [7] Star- delta starter of an induction motor A. Inserts resistance in rotor circuit B. Inserts resistance in stator circuit C. Applies reduced voltage to rotor D. Applies reduced voltage to stator [8] The starting torque of a 1-phase induction motor is A. High B. Medium C. Low D. Zero [9] The thrust developed by a linear induction motor depends on A. Synchronous speed B. Rotor input C. Number of poles D. both A and B [10]A 3-phase squirrel cage induction motor supplied from a balanced 3-phase source drives a mechanical load. The torque-speed characteristics of the motor (solid curve) and of the load (dotted curve) are shown. Of the two equilibrium points A and B, which of the following options correctly describes the stability of A and B? [GATE 2009] A.A is stable B is unstable B.A is unstable B is stable C.Both are stable D.Both are unstable


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P.M.MEVADA

2.5 – SYNCHRONOUS MOTOR

[1] In a synchronous motor, damper winding is provided to A. Stabilize rotor motion B. Suppress rotor oscillations C. Develop necessary starting torque D. Both B and C [2] Synchronous capacitor is A. An ordinary static capacitor bank B. An over excited synchronous motor driving mechanical load C. An over excited synchronous motor running without mechanical load D. None of the above [3] A synchronous machine is called as doubly excited machine because A. It can be over excited B. It has two sets of rotor poles C. Both its rotor and stator are excited D. It needs twice the normal exciting current [4]If the field of a synchronous motor is under excited, the power factor will be A. Lagging B. Leading C. Unity D. More than unity [5] The direction of rotation of a synchronous motor can be reversed by reversing A. Current to the field winding B. Supply phase sequence C. Polarity of rotor poles D. None of the above [6]A synchronous motor connected to infinite busbars has at constant full-load, 100% excitation and unity pf. On changing the excitation only, the armature current will have A. leading pf with under-excitation B. leading pf with over excitation C. lagging pf with over excitation D. no change of pf [7] The maximum value of torque angle a in a synchronous motor is.......degrees electrical A. 45 B. 90 C. between 45 and 90 D. below 60 [8] The angle between the synchronous rotating stator flux and rotor poles of a synchronous motor is A. Synchronizing angle


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P.M.MEVADA B. Torque angle C. Power factor angle D. Slip angle [9] In a synchronous machine when the rotor speed becomes more than the synchronous speed during hunting, the damping bars develop A. synchronous motor torque B. dc motor torque C. induction motor torque D. induction generator torque [10] When load on a synchronous motor is increased its armature current is increased provided it is A. normally excited B. over excited C. under exciter D. all of the above

2.6 – GENERAL ELECTRICAL MACHINE [1]A field excitation of 20A in a certain alternator results in an armature current of 400A in short circuit and a terminal voltage of 2000V on open circuit. The magnitude of the internal voltage drop within the machine at a load current of 200A is [GATE2009] A.1V B.10V C.100V D.1000V [2] Figure shows the extended view of a 2 pole dc machine with 10 armature conductors.Normal brush positions are shown by A and B, placed at the interpolar axis. If the brushes are now shifted, in the direction of rotation, to A' and B' as shown, the voltage waveform VA'B' will resemble. [GATE]

Ans: A


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P.M.MEVADA [3]A 220V,50Hz,single-phase induction motor has the following connection diagram and winding orientations shown.MM' is the axis of the main stator winding(M 1M2) and AA' is that of the auxiliary winding (A1A2). Directions of the winding axes indicate direction of flux when currents in the windings are in the directions shown. Parameters of each winding are indicateD. When switch S is closed, the motor [GATE]

A. rotates clockwise B. rotates anticlockwise C. does not rotate D. rotates momentarily and comes to a halt [4] The electromagnetic torque Te of a drive, and its connected load torque Tl are as shown below. Out of the operating points A,B, C and D, the stable ones are [GATE 2007]

Ans:C [5] In a transformer, zero voltage regulation at full load is [GATE 2007] A. Not possible B. Possible at unity Power factor load C. Possible at leading Power factor load D. Possible at lagging Power factor load [6] The DC motor, which can provide zero speed regulation at full load without any controller is [GATE 2007] A. Series B. Shunt C. Cumulative Compound D. Differential Compound [7] A single phase 10kVA, 50 Hz transformer with 1kV primary winding draws 0.5A and 55W, at rated voltage and frequency, on no loaD. A second transformer has a core with all its linear √2 times the corresponding dimensions of the first transformer. The core material and lamination thickness are the same in both transformers. The primary windings of both the transformers have the same number of turns. If a rated voltage of 2kV at 50Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are [GATE2012] A. 0.7 A,77.8W B. 0.7A,155.6 W C. 1A,110W D. 1A,220W


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P.M.MEVADA [8] The locked rotor current in a 3-phase, star connected 15kW, 4-pole, 230V, 50Hz induction motor at rated conditions is 50A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236V, 57Hz supply is [GATE2012] A. 58.5A B. 45.0A C. 45.7A D. 55.6A [9] A 220V, 15kW,1000rpm shunt motor with armature resistance of 0.25Ω, has a rated line current of 68A and a rated field current of 2.2A. The change in field flux required to obtain a speed of 1600 rpm while drawing a line current of 52.8A and a field current of 1.8A is [GATE2012] A. 18.18% increase B. 18.18% decrease C. 36.36% increase D. 36.36% decrease [10] In 8 - pole wave connected motor armature, the number of parallel paths are A. 8 B. 4 C. 2 D. 1 [11] A salient pole synchronous motor is running at no loaD. Its field current is switched off. The motor will (A) come to stop. (B) continue to run at synchronous speeD. (C) continue to run at a speed slightly more than the synchronous speeD. (D) continue to run at a speed slightly less than the synchronous speeD. [12] The emf induced in the primary of a transformer (A) is in phase with the flux. (B) lags behind the flux by 90 degree. (C) leads the flux by 90 degree. (D) is in phase opposition to that of flux. [13]The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load speed is about (A) 50 Hz. (B) 20 Hz. (C) 2 Hz. (D) Zero. [14] The two windings of a transformer is (A) conductively linked. (B) inductively linked. (C) not linked at all. (D) electrically linked. [15] The D.C. series motor should always be started with load because (A) at no load, it will rotate at dangerously high speeD. (B) it will fail to start. (C) it will not develop high starting torque. (D) all are true. [16] Out of the following methods of heating the one which is independent of supply frequency is (A) electric arc heating (B) induction heating (C) electric resistance heating (D) dielectric heating [17] In a stepper motor the angular displacement (A) can be precisely controlled. (B) it cannot be readily interfaced with micro computer based controller. (C) the angular displacement cannot be precisely controlled.


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P.M.MEVADA (D) it cannot be used for positioning of work tables and tools in NC machines. [18] The generation voltage is usually (A) between 11 KV and 33 KV. (B) between 132 KV and 400 KV. (C) between 400 KV and 700 KV. (D) None of the above. [19] When a synchronous motor is running at synchronous speed, the damper winding produces (A) damping torque. (B) eddy current torque. (C) torque aiding the developed torque. (D) no torque. [20] A hysteresis motor (A) is not a self-starting motor. (B) is a constant speed motor. (C) needs dc excitation. (D) can not be run in reverse speed. [21] If a transformer primary is energized from a square wave voltage source, its output voltage will be (A) A square wave. (B) A sine wave. (C) A triangular wave. (D) A pulse wave. [22] The power factor of a squirrel cage induction motor is (A) low at light load only. (B) low at heavy load only. (C) low at light and heavy load both. (D) low at rated load only. [23] In a D.C. machine, the armature mmf is (A) stationary w.r.t. armature. (B) rotating w.r.t. field. (C) stationary w.r.t. field. (D) rotating w.r.t. brushes. [24] In a transformer the voltage regulation will be zero when it operates at (A) unity p.f. (B) leading p.f. (C) lagging p.f. (D) zero p.f. leading. [25] The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be (A) 3.6 V. (B) 2.5 V. (C) 3.0 V. (D) 6.0 V. [26] The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for a (A) dc machine. (B) 3 phase induction machine. (C) synchronous machine. (D) single phase induction machine. Ans: All are correct [27] The current from the stator of an alternator is taken out to the external load circuit through (A) slip rings. (B) commutator segments. (C) solid connections. (D) carbon brushes.


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P.M.MEVADA [28] A motor which can conveniently be operated at lagging as well as leading power factors is the (A) squirrel cage induction motor. (B) wound rotor induction motor. (C) synchronous motor. (D) DC shunt motor. [29] The most suitable servomotor for low power applications is (A) a dc series motor. (B) a dc shunt motor. (C) an ac two-phase induction motor. (D) an ac series motor. [30] The size of a conductor used in power cables depends on the (A) operating voltage. (B) power factor. (C) current to be carried. (D) type of insulation used. [31]The size of the feeder is determined primarily by (A) the current it is required to carry. (B) the percent variation of voltage in the feeder. (C) the voltage across the feeder. (D) the distance of transmission. [32] The emf induced in the primary of a transformer (A) is in phase with the flux. (B) lags behind the flux by 90 degree. (C) leads the flux by 90 degree. (D) is in phase opposition to that of flux. [33] The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for a (A) dc machine. (B) 3 phase induction machine. (C) synchronous machine. (D) single phase induction machine. Ans: all options are correct [34]As the voltage of transmission increases, the volume of conductor (A) increases. (B) does not change. (C) decreases. (D) increases proportionately. HINT:-Due to skin effect [35]In a 3-phase synchronous motor (A) the speed of stator MMF is always more than that of rotor MMF. (B) the speed of stator MMF is always less than that of rotor MMF. (C) the speed of stator MMF is synchronous speed while that of rotor MMF is zero. (D) rotor and stator MMF are stationary with respect to each other. HINT:-Motor is magnetically locked into position with stator, the rotor poles are engaged with stator poles and both run synchronously in same direction. [36]An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be (A) less. (B) more. (C) more or less. (D) the same. HINT:-Over excitation gives leading power factor and under excitation gives lagging p.f . [37] Out of the following methods of heating the one which is independent of supply frequency is (A) electric arc heating (B) induction heating


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P.M.MEVADA (C) electric resistance heating (D) dielectric heating [38]In a capacitor start single-phase induction motor, the capacitor is connected (A) in series with main winding. (B) in series with auxiliary winding. (C) in series with both the windings. (D) in parallel with auxiliary winding. HINT:-To make single phase motor self start. We split the phases at 90 degree. Hence, motor behaves like a two phase motor. [39]A synchro has (A) a 3-phase winding on rotor and a single-phase winding on stator. (B) a 3-phase winding on stator and a commutator winding on rotor. (C) a 3-phase winding on stator and a single-phase winding on rotor. (D) a single-phase winding on stator and a commutator winding on rotor. HINT:-The basic synchro unit called a synchro transmitter. It’s construction similar to that of a Three phase alternator. [40] A ceiling fan uses (A) split-phase motor. (B) capacitor start and capacitor run motor. (C) universal motor. (D) capacitor start motor. HNIT:-To give starting torque and to maintain speed. [41] The torque-speed characteristics of an A.C. operated universal motor has a ______characteristic and it______ be started under no-load condition. (A) inverse, can (B) nearly inverse, can (C) inverse, cannot (D) nearly inverse, cannot HINT:-N direct proportional to 1/ T [42] In the heating process of the ________type a simple method of temperature control is possible by means of a special alloy which loses its magnetic properties at a particular high temperature and regains them when cooled to a temperature below this value. (A) Indirect induction over (B) core type induction furnace (C) coreless induction furnace (D) high frequency eddy current HINT:-Magnetic property of alloy changes with change of the temperature and Heat is produced due to eddy current = Square(i) * R and i proportional to square(f) [43] In order to reduce the harmful effects of harmonics on the A.C. side of a high voltage D.C. transmission system ______are provideD. (A) synchronous condensers (B) shunt capacitors (C) shunt filters (D) static compensators HINT:Xc= 1/ωC [44]An A.C. tachometer is just a ________with one phase excited from the carrier frequency. (A) two-phase A.C. servomotor (B) two-phase induction motor (C) A.C. operated universal motor (D) hybrid stepper motor. HINT:-It is a special purpose machine. It's stator coil can be energized by electronically switched current. [45] The rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of 0.04 is________Hz


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P.M.MEVADA (A) 8 (B) 4 (C) 6 (D) 2 HINT:f = N P/ 120 = 1000* 6/120 = 50 Hz Rotor frequency fr=s * f = 0.04 * 50= 2.0 Hz [46] The speed-torque characteristics of a DC series motor are approximately similar to those of the _________motor. (A) universal (B) synchronous (C) DC shunt (D) two-phase HINT:-Universal motor has same characteristics as DC series motor It is known as an A.c series motor. [47]In case of a universal motor, torque pulsation is minimized by _________. (A) load inertia (B) rotor inertia (C) both rotor and load inertia (D) none of the above [48] A hysteresis motor (A) is not a self-starting motor. (B) is a constant speed motor. (C) needs dc excitation. (D) can not be run in reverse speed. [49] The most suitable servomotor for low power applications is (A) a dc series motor. (B) a dc shunt motor. (C) an ac two-phase induction motor. (D) an ac series motor. [50] The size of a conductor used in power cables depends on the (A) operating voltage. (B) power factor. (C) current to be carried. (D) type of insulation used. [51]A stepper motor is (A) a dc motor. (B) a single-phase ac motor. (C) a multi-phase motor. (D) a two phase motor. HINT:-Stepper motor works on 1-phase-ON or 2-phase –ON modes of operation [52] A motor which can conveniently be operated at lagging as well as leading power factors is the (A) squirrel cage induction motor. (B) wound rotor induction motor. (C) synchronous motor. (D) DC shunt motor. [53] The D.C. series motor should always be started with load because (A) at no load, it will rotate at dangerously high speed. (B) it will fail to start. (C) it will not develop high starting torque. (D) all are true. [54] The ‘sheath’ is used in cable to (A) provide strength to the cable. (B) provide proper insulation. (C) prevent the moisture from entering the cable.


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P.M.MEVADA (D) avoid chances of rust on strands. HINT:-The sheath in underground cable is provided to give mechanical strength. [55] The drive motor used in a mixer-grinder is a (A) dc motor. (B) induction motor. (C) synchronous motor. (D) universal motor. HINT:-The universal motor is suitable for AC & DC both supply systems. [56] A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is (A) 1500 r.p.m. (B) 1425 r.p.m. (C) 25 r.p.m. (D) 75 r.p.m. HINT:-NS = 120f /P = 120 x 50 /4 =1500rpm N = NS ( 1-s) = 1500 (1-0.05) = 1425 Relative speed = 1500 – 1425 = 75 rpm [57] The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be (A) 3.6 V. (B) 2.5 V. (C) 3.0 V. (D) 6.0 V. [58] The current from the stator of an alternator is taken out to the external load circuit throu (A) slip rings. (B) commutator segments. (C) solid connections. (D) carbon brushes. [59] In a 3 – phase induction motor the maximum torque (A) is proportional to rotor resistance r2 . (B) does not depend on r2 . (C) is proportional to square root of r2 . (D) is proportional to square of r2 . [60] In a D.C. machine, the armature mmf is (A) stationary w.r.t. armature. (B) rotating w.r.t. field. (C) stationary w.r.t. field. (D) rotating w.r.t. brushes. [61] In a transformer the voltage regulation will be zero when it operates at (A) unity p.f. (B) leading p.f. (C) lagging p.f. (D) zero p.f. leading. [62] In a stepper motor the angular displacement (A) can be precisely controlled. (B) it cannot be readily interfaced with micro computer based controller. (C) the angular displacement cannot be precisely controlled. (D) it cannot be used for positioning of work tables and tools in NC machines. [63] The power factor of a squirrel cage induction motor is (A) low at light load only. (B) low at heavy load only. (C) low at light and heavy load both. (D) low at rated load only. [64] The generation voltage in India is usually


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P.M.MEVADA (A) between 11 KV and 33 KV. (B) between 132 KV and 400 KV. (C) between 400 KV and 700 KV. (D) None of the above. [65] When a synchronous motor is running at synchronous speed, the damper winding produces (A) damping torque. (B) eddy current torque. (C) torque aiding the developed torque. (D) no torque. [66]If a transformer primary is energised from a square wave voltage source, its output voltage will be (A) A square wave. (B) A sine wave. (C) A triangular wave. (D) A pulse wave. [67] A salient pole synchronous motor is running at no load. Its field current is switched off. The motor will (A) come to stop. (B) continue to run at synchronous speed. (C) continue to run at a speed slightly more than the synchronous speed. (D) continue to run at a speed slightly less than the synchronous speed. [68] The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load speed is about (A) 50 Hz. (B) 20 Hz. (C) 2 Hz. (D) Zero. [69] The speed of a dc motor can be controlled by varying A. its flux per pole B. resistance of armature circuit C. applied voltage D. all of the above [70] Regarding Ward-Leonard system of speed control which statement is false? A. It is usually used where wide and very sensitive speed control is required B. It is used for motors having ratings from 750kW to 4000Kw C. Capital outlay involved in the system is right since it uses two extra machines D. It gives a speed range of 10:1 but in one direction only E. It has low overall efficiency especially at light loads [71] In a DC motor, unidirectional torque is produced with the help of A. Brushes B. Commutator C. End-plates D. Both a and b [72] The counter emf of dc motor A. Often exceeds the supply voltage B. Aids the applied voltage C. Helps in energy conversion D. Regulates its armature voltage [73] The Eb/V ratio of a dc motor is an indication of its A. Efficiency B. Speed regulation C. Starting torque D. Running Torque [74] The induced emf in the armature conductors of a dc motor is A. Sinusoidal B. Trapezoidal C. Rectangular


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P.M.MEVADA D. Alternating [75] A dc motor can be looked upon as dc generator with the power flow A. Reduced B. Reversed C. Increased D. Modified [76] A series motor is best suited for driving A. Lathes B. Cranes and hoists C. Shears and punches D. Machine tools [77]The Ta/Ia graph of a dc series motor is a A. Parabola from no load to overload B. Straight line throughout C. Parabola throughout D. Parabola upto full load and a straight line at overloads [78] When load is removed, .......motor will run at the highest speed. A. Shunt B. Cumulative – compound C. Differential compound D. Series [79] The power factor of a squirrel cage induction motor is A. Low at light loads only B. Low at heavy loads only C. Low at light and heavy loads both D. Low at rated load only [80] The synchronous speed of a linear induction motor does not depend on A. Width of pole pitch B. Number of poles C. Supply frequency D. Any of the above


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P.M.MEVADA

CHAPTER-3. TRANSFORMERS [1] A Buchholz relay can be installed on A. Auto-transformers B. Air-cooled transformers C. Welding transformers D. Oil cooled transformers [2] The chemical used in breather is A. Asbestos fibre B. Silica sand C. Sodium chloride D. Silica gel [3] Material used for construction of transformer core is usually A. 0.4mm to 0.5 mm B. 4mm to 5 mm C. 14mm to 15 mm D. 25mm to 40 mm [4] Helical coils can be used on A. Low voltage side of high kVA transformers B. High frequency transformers C. High voltage side of small capacity transformers D. High voltage side of high kVA rating transformers [5] The transformer ratings are usually expressed in terms of A. Volts B. Amperes C. kW D. kVA [6] The value of flux involved in the emf equation of a transformer is A. rms value B. rms value C. Maximum value D. Instantaneous value [7] The main advantage of auto transformer over a two winding transformer is A. Hysteresis losses are reduced B. Saving in winding material C. Copper losses are negligible D. Eddy losses are totally eliminated [8] During short circuit test iron losses are negligible because A. The current on secondary side is negligible B. The voltage on secondary side does not vary C. The voltage applied on primary side is low D. Full-load current is not supplied to the transformer [9] Which of the following properties is not necessarily desirable in the material for transformer core? A. Mechanical strength B. Low hysteresis loss C. High thermal conductivity D. High permeability [10] The main reason for generation of harmonics in a transformer could be A. Fluctuating load B. Poor insulation C. Mechanical vibrations D. Saturation of core [11] A transformer transforms A. frequency B. voltage


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P.M.MEVADA C. current D. voltage and current [12] Which is not the basic element of the transformer? A. core B. primary winding C. secondary winding D. mutual flux [13] In an ideal transformer A. windings have no resistance B. core has no losses C. core has infinite permeability D. all of the above [14] The frequency of the secondary voltage of a transformer will be..... A. less than frequency of the primary voltage B. equal to the primary voltage C. greater than the frequency of the primary voltage D. much greater than the frequency of the primary voltage [15] The efficiency of a transformer is maximum when A. It runs at half full load B. it runs at full load C. its Cu loss equal iron loss D. it runs over load [16] A step-up transformer increases A. voltage B. current C. power D. frequency [17] Which type of loss is not common to transformer and rotating machines? A. Eddy current loss B. Copper loss C. Hysteresis loss D. Windage loss [18] The transformer core is laminated to A. Reduce the copper losses B. Reduce the core losses C. Reduce the eddy current losses D. None of the above [19] Transformer cores are built up from laminations rather than from solid metal so that A. Oil penetrates the core more easily B. Eddy current loss is reduced C. Less lamination is required for the windings D. Turn ratio is higher than voltage ratio [20] the main purpose of using core in a transformer is to A. Decrease iron losses B. prevent eddy current loss C. eliminate magnetic hysteresis D. decrease reluctance of the common magnetic circuit [21] The ordinary two winding transformer's primary and secondary windings always have A. different no of turns B. same size of copper wire C. a common magnetic circuit D. separate magnetic circuits [22] No load test on a transformer is carried out to find A. copper loss B. magnetising current


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P.M.MEVADA C. magnetising current and no load loss D. efficiency of the transformer [23] Transformers are rated in KVA instead of KW because A. load power factor is often not known B. KVA is fixed whereas KW depends on load power factor C. Total transformer loss depends on volt ampere D. It has become customary [24] Transformer cores are laminated in order to A. simplify its construction B. minimise eddy current loss C. reduce cost D. reduce hysteresis loss [25] A step up transformer increases A. voltage B. current C. power D. frequency [26] In a two winding transformer, the primary and secondary induced emf E1 & E2 are always A. equal in magnitude B. anti phase with each other C. in phase with each other D. determined by load on transformer secondary [27] In a transformer, the leakage flux of each winding is proportional to the current in that winding because A. Ohm's law applies to magnetic circuits B. Leakage paths do no saturate C. the two windings are electrically isolated D. mutual flux is confined to the core [28] In a two winding transformer, the emf /turn in secondary winding is always......the induced emf power turn in primary A. equal to k times B. equal to 1/k times C. equal D. greater than [29] In transformer terminology, the ratio 20:1 indicates that A. there are 20 turns on primary one turn on secondary B. secondary voltage is 1/20th of the primary C. primary current is 20 times greater than the secondary current D. for every 20 turns on primary, there is one turn on secondary [30] In performing the short circuit test of a transformer A. high voltage is usually short circuited B. low voltage side is usually short circuited C. any side is short circuited with preference D. none of the above Common Data for Questions 1 and 2: [GATE 2009] The star-delta transformer shown above is excited on the star side with a balanced,4-wire,3-phase,sinusoidal voltage supply of rated magnitude. The transformer is under no load condition.


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P.M.MEVADA

[31] With both S1 and S2 open, the core flux waveform will be [GATE 2009] A. a sinusoidal at fundamental frequency B. flat-topped with third harmonic C. peaky with third-harmonic D. none of these [32] With S2 closed and S1 open, the current waveform in the delta winding will be [GATE 2009] A. a sinusoidal at fundamental frequency B. flat-topped with third harmonic C. only third-harmonic D. none of these Common Data for Questions 3 and 4: The circuit diagram shows a two-winding, losses transformer with no leakage flux, excited from a current source,i(t),whose waveform is also shown. The transformer has a magnetizing inductance of 400/ πmH.

[33] The peak voltage across A and B, with S open is [GATE 2009] A. 400/ πV B. 800 πV C. 4000/π V D. 800/ πV [34] If the waveform of i(t) is changed to i(t)= 10 sin(100πt)A, the peak voltage across A and B with S closed is [GATE 2009] A. 400V B. 240V C. 320V D. 160V Statement for Linked Answer Questions 5 and 6: [GATE 2009]

The figure above shows coils 1 and 2, with dot markings as shown, having 4000 and 6000 turns respectively. Both the coils have a rated current of 25A. Coil 1 is excited with single phase, 400V, 50Hz supply. [35] The coils are to be connected to obtain a single phase, 400/1000V, auto-transformer to drive a load of 10kVA. Which of the options given should be exercised to realize the required auto-transformer? [GATE 2009] A. Connect A and D; Common B B. Connect B and D; Common C


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P.M.MEVADA C. Connect A and C; Common B D. Connect A and C; Common D [36] In the autotransformer obtained in Question 57, the current in each coil is [GATE 2009] A. Coil-1 is 25A and Coil-2 is 10A B. Coil-1 is 10A and Coil-2 is 25A C. Coil-1 is 10A and Coil-2 is 15A D. Coil-1 is 15A and Coil-2 is 10A [37]The single phase, 50Hz iron core transformer in the circuit has both the vertical arms of cross sectional area 20cm2 and both the horizontal arms of cross sectional area 10cm2. If the two windings shown were wound instead on opposite horizontal arms, the mutual inductance will [GATE 2009]

A.Double B.Remain same C.Be halved D.Become one quarter Ans:[38] In a transformer the energy is conveyed from primary to secondary? A. Through cooling coil B. Through air C. By the flux D. None of the above [39] Which loss is not common between a transformer and rotating machines? A. Eddy current loss B. Copper loss C. Windage loss D. Hysteresis loss [40] No load test on a transformer is carried out to find A. Copper loss B. magnetising current C. Magnetising current and loss D. Efficiency of the transformer [41] Sumpner's test is conducted on transformers to find A. Temperature B. Stray losses C. All-day efficiency D. None of the above [42] The efficiency of a transformer will be maximum when A. copper losses = hysteresis losses B. Hysteresis losses = eddy current losses C. Eddy current losses = copper losses D. Copper losses = iron losses [43] The purpose of providing an iron core in a transformer is to A. Provide support to windings


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P.M.MEVADA B. Reduce hysteresis loss C. decrease the reluctance of the magnetic path D. reduce eddy current losses [44] The highest voltage for transmitting electrical power in India is A. 33kV B. 66kV C. 132kV D. 400kV [45] The function of conservator in a transformer is A. To protect against internal fault B. To reduce copper as well as core losses C. To cool the transformer oil D. To take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings [46] The core used in high frequency transformer is usually A. Copper core B. Cost iron core C. Air core D.Mid steel core [47] Cross over windings are used in A. Low voltage side of high kVA rating transformers B. Current transformers C. High voltage side of high kVA rating transformers D. High voltage side of low kVA rating transformers [48] During light loads, the transformer efficiency is low because A. Secondary output is low B. Transformer losses are high C. Fixed loss is high in proportion to the output D. Cu loss is small [49] The open circuit test is carried out in a transformer to find the A. Cu loss B. Core loss C. Total loss D. Insulation resistance [50] The equivalent resistance of the primary of the transformer having K = 5, R1 = 0.1 ohm when referred to secondary becomes .....ohm A. 0.5 B. 0.02 C. 0.004 D. 2.5 [51] A transformer has negative voltage regulation when its load power factor is A. Zero B. Unity C. Leading D. Lagging [52] A transformer has 1000 primary turns, connected to 250V ac supply. To get 400V secondary voltage the no of secondary turns should be A. 1600 B. 250 C. 400 D. 1250


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P.M.MEVADA [53] The iron loss of the transformer is negligible during short circuit test because A. The entire input is just sufficient to meet Cu losses only B. Flux produced is a small fraction of the normal flux C. Iron core becomes fully saturated D. Supply frequency is held constant [54] In operating a 400hz transformer at 50Hz A. Only voltage is reduced in the same proportion as the frequency B. Only KVA rating is reduced in the same proportion as the frequency C. Both voltage and KVA rating are reduced in the same proportion as frequency D. None of the above [55] When a 400Hz transformer is operated at 50Hz its KVA rating is A. Reduced to 1/8 B. Increased 8 times C. Unaffected D. Increased 64 times [56] Which of the following does not change in a transformer? A. Current B. Voltage C. Frequency D. All of the above [57] In a transformer the resistance between its primary and secondary is A. Zero B. 1Ω C. 1000 Ω D. Infinite [58] If a pump motor is run on 2/3rd of its supply voltage, it will A. Continue to deliver same power B. burn C. stall D. continue to run at lower speed [59] An ideal transformer has infinite values of primary and secondary inductances. The statement is A. True B. False [60] The noise resulting from vibrations of laminations set by magnetic force, is termed as A. magnetostriction B. boo C. hum D. zoom [61] The degree of mechanical vibrations produced by the laminations of a transformers depends on A. Tightness of clamping B. Gauge of laminations C. Size of laminations D. All of the above [62] The no-load current drawn by transformer is usually........percent of the full-load current? A. 0.2 to 0.5 % B. 2 to 5% C. 12 to 15 % D. 20 to 30 % [63] The dielectric strength of transformer oil is expected to be A. 1kV B. 33kV C. 100kV D. 330 kV [64] During the short-circuit test on a small transformer the frequency is increased from 50-200Hz. The copper losses will increase by a factor of


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P.M.MEVADA A. 16 B. 4 C. 1 D. 1/4 [65] No-load current in a transformer A. Lags behind the voltage by about 75 deg B. leads the voltage by about 75 C. lags behind the voltage by about 15 D. leads the voltage by about 15 [66] While conducting short-circuit test on a transformer the following side is short circuited A. High voltage side B. low voltage side C. primary side D. secondary side [67] The chemical used in breather for transformer should have the quality of A. Ionizing air B. Absorbing moisture C. Cleansing the transformer oil D. Cooling the transformer oil [68] The path of a magnetic flux in a transformer should have A. High resistance B. High reluctance C. Low resistance D. Low reluctance [69] In case there are burrs on the edges of the laminations of the transformer, it is likely to result in A. Vibrations B. Noise C. Higher eddy currents loss D. Higher hysteresis loss [70] Silicon steel used in laminations mainly reduces A. Hysteresis loss B. Eddy current losses C. Copper loss D. All of the above [71] High frequency transformers sometimes make use of ferrite cores because it has A. High specific gravity B. High resistance C. High hysteresis D. low permeability [72] Harmonics in transformer result in A. Increased core losses B. Increased I2R losses C. Magnetic interference with communication circuits D. All of the above [73] The full load copper loss of a transformer is 1600W. At half-load the copper loss will be A. 6400W B. 1600W C. 800W D. 400W [74] Power transformers are generally designed to have maximum efficiency around A. No load B. Half load C. Near full load D. 10% overload


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P.M.MEVADA [75] Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results A. Short-circuiting of the secondaries B. Power factor of one of the transformers is leading while that of the other lagging C. Transformers having higher copper losses will have negligible core losses D. Loading of the transformers not in proportion to their kVA ratings. [76] The changes in volume of transformer cooling oil due to variation of atmospeheric temperature during day and night is taken care of by which part of transformer? A. Conservator B. Breather C. Bushings D. Buchholz relay [77] The transformer laminations are insulated from each other by A. Mica strip B. Thin coat of varnish C. Paper D. Any of the above [78] Which type of winding is used in 3 phase shell type transformer? A. Circular type B. Sandwich type C. Cylindrical type D. Rectangular type [79] During open circuit test of a transformer A. Primary is supplied rated voltage B. Primary is supplied full load current C. Primary is supplied current at reduced voltage D. Primary is supplied rated kVA [80] Which of the following is not standard voltage for power supply in India A. 11kV B. 33kV C. 66 kV D. 122 kV [81] A transformer core is laminated to A. Reduce hysteresis loss B. Reduce eddy current losses C. Reduce copper losses D. Reduce all above losses [82] While conducting short-circuit test on a transformer the following side is short-circuited A. High voltage side B. Low voltage side C. Primary side D. Secondary side [83] Distribution transformers are generally designed for maximum efficiency around A. 90% load B. Zero load C. 25% load D. 50% load [84] A transformer oil must be free from A. Sludge B. Odour C. Gases D. Moisture


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P.M.MEVADA [85] The use of higher flux density in the transformer design A. Reduces weight per KVA B. Reduces iron losses C. Reduces copper losses D. Increases part load efficiency [86] In a transformer the toppings are generally provided on A. Primary side B. Secondary side C. Low voltage side D. High voltage side [87] Which of the following is not a part of transformer installation? A. Conservator B. Breather C. Buchholz relay D. Exciter


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P.M.MEVADA

CHAPTER-4. POWER SYSTEM [1]Three generators are feeding a load of 100MW.The details of the generators are Rating(MW) Efficiency() Regulation(p.u.) on 100MVA base Generator-1 100 20 0.02 Generator-2 100 30 0.04 Generator-3 100 40 0.03 In the event of increased load power demand, which of the following will happen? [GATE 2009] A. All the generators will share equal power B.Generator – 3 will share more power compared to Generator – 1 C.Generator – 1 will share more power compared to Generator – 2 D.Generator – 2 will share more power compared to Generator – 3 Ans: None of the above [2]A 500MW, 21kV, 50Hz, 3-phase, 2-pole synchronous generator having a rated p.f. =0.9, has a moment of inertia of 27.5 x 103 kg-m2. The inertia constant (H) will be [GATE 2009] A.2.44 s B.2.71s C.4.88s D.5.42s [3]For a fixed value of complex power flow in a transmission line having a sending end voltage V, the real power loss will be proportional to [GATE 2009] A.V B.V2 C.1/V2 D.1/V [4]How many 200W/220V incandescent lamps connected in series would consume the same total power as a single 100W/220V incandescent lamps? [GATE 2009] A.Not possible B.4 C.3 D.2 [5]Match the items in list I with the items in list II and select the correct answer using the codes given below the lists [GATE 2009] LIST 1 LIST2 TO USE A.improve power factor 1.shunt reactor B.reduce the current ripples 2.shunt capacitor C.increase the power flow in line 3.series capacitor D.reduce the ferranti effect 4.series reactor A. a→2,b→3,c→4,d→1 B. a→2,b→4,c→3,d→1 C. a→4,b→3,c→1,d→2 D. a→4,b→1,c→3,d→2 [6]Match the items in list I with the items in list II and select the correct answer using the codes given below the lists [GATE 2009] LIST 1 LIST2 Type of Transmission Line Type of Distance Relay Preferred A.short line 1.Ohm Relay B.Medium line 2.Reactance Relay C.Long line 3.Mho Relay A. a→2,b→1,c→3 B. a→3,b→2,c→1 C. a→1,b→2,c→3 D. a→1,b→3,c→2


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P.M.MEVADA [7] For the system shown below, SD1 and SD2 are complex power demands at bus 1 and bus 2 respectively. If |V2|=1pu, the VAR rating of the capacitor (QG2) connected at bus 2 is [GATE2012]

A. 0.2 pu B. 0.268 C. 0.312 D. 0.4pu [8] A cylindrical rotor generator delivers 0.5 pu power in the steady-state to an infinite bus through a transmission line of reactance 0.5 pu. The generator no-load voltage is 1.5 pu and the infinite voltage is 1.5 pu. The inertia constant of the generator is 5MW-s/MV and the generator reactance is 1 pu.The critical clearing angle, in degrees, for a three-phase dead short circuit fault at the generator terminal is [GATE2012] A. 53.5 B. 60.2 C. 70.8 D. 79.6 [9] Power is transfered from system A to system B by an HVDC link as shown in the figure.If the voltages VAB and VCD are as indicated in the figure, and I>0,then

A. VAB<0,VCD<0,VAB>VCD B. VAB>0,VCD>0,VAB>VCD C. VAB>0,VCD>0,VAB0,VCD<0 [10] Consider a step voltage wave of magnitude 1pu travelling along a lossless transmission line that terminates in a reactor.The voltage magnitude across the reactor at the instant the travelling wave reaches the reactor is

A. -1pu B. 1pu C. 2pu D. 3pu


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P.M.MEVADA [11] Consider two buses connected by an impedance of (0+j5)Ω. The bus 1 voltage is 100∠30° V, and bus 2 voltage is 100∠0° V. The real and reactive power supplied by bus 1, respectively are A. 1000W,268Var B. -1000W,-134Var C. 276.9W,-56.7Var D. -276.9W,56.7Var [12] A three-phase, 33kV oil circuit breaker is rated 1200A, 2000MVA, 3s. The symmetrical breaking current is A. 1200A B. 3600A C. 35kA D. 104.8kA [13] Consider a stator winding of an alternator with an internal high-resistance ground fault.The currents under the fault condition are as shown in the figure.The winding is protected using a differential current scheme with current transformers of ratio 400/5A as shown. The current through the operating coil is

A. 0.17875A B. 0.2A C. 0.375A D. 60kA [14] A 50Hz synchronous generator is initially connected to a long lossless transmission line which is open circuited at the receiving enD.With the field voltage held constant, the generator is disconnected from the transmission line.Which of the following may be said about the steady state terminal voltage and field current of the generator?

A. The magnitude of terminal voltage decreases,and the field current does not change B. The magnitude of terminal voltage increases,and the field current does not change C. The magnitude of terminal voltage increases,and the field current increases D. The magnitude of terminal voltage does not change,and the field current decreases Ans: none of the above [15] For enhancing the power transmission in a long EHV transmission line, the most preferred method is to connect a A. series inductive compensator in the line B. shunt inductive compensator at the receiving end C. series capacitive compensator in the line D. shunt capacitive compensator at the sending end


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P.M.MEVADA [16] Consider a three-phase,50Hz,11kV distribution system.Each of the conductors is suspended by an insulator string having two identical porcelain insulators.The self capacitance of the insulator is 5 times the shunt capacitance between the link and the ground,as shown in the figure.The voltage across the two insulators is

A. e1=3.74kV,e2=2.61kV B. e1=3.46kV,e2=2.89kV C. e1=6.0kV,e2=4.23kV D. e1=5.5kV,e2=5.5kV [17] Consider a three-core, three-phase,50Hz,11kV cable whose conductors are denoted as R,Y and B in the figure.The inter-phase capacitance(C1) between each pair of conductors is 0.2μF and the capacitance between each line conductor and the sheath is 0.4μF.The per-phase charging current is

A. 2.0A B. 2.4A C. 2.7A D. 3.5A [18] For the power system shown in the figure below,the specifications of the components are the following: G1: 25kV,100MVA,X=9% G2: 25'kV,100MVA,X=9% T1: 25kV/220kV,90MVA,X=12% T2: 220kV/25kV,90MVA,X=12% Line1: 220kV, X=150 ohms.

Choose 25kV as the base voltage at the generator G1 and 200MVA as the MVA base.The impedance diagram is.....Options A,B,C,D are given below


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P.M.MEVADA

[A]

[B]

[C]

[D] Ans:B


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P.M.MEVADA

CHAPTER-5. POWER ELECTRONICS [1] A 240V, 50Hz supply feeds a highly inductive load of 50 Ohm resistance through a half controlled thyristor bridge. When the firing angle α=45°, the load power is A. 418 W B. 512 W C. 367 W D. 128 W Exp: Vav = (Vm/π) (1 + cosα) = [(√2*240)/(π) ) ( 1 + cos45)] = 184.4 V Iav = Vav / R = 184.4/50 =3.69A

= 3.69 * √[(180 -45)/180] = 3.2A P = 3.2 * 3.2 *50 = 512 W .................................................................................................................................................................................................................................. [2] A D.C. to D.C. chopper operates from a 48 V battery source into a resistive load of 24Ohm. The frequency of the chopper is set to 250Hz. When chopper on-time is 1 ms the load power is A. 6W B. 12W C. 24W D. 48W Exp: Vavg = V* f * Ton = 48 x 250 x (10 - 3) = 12V Iav = Vav/R = 12/24 = 0.5A Vrms= V* Square root (Ton) * f = 48 * Square root (0.25) = 24V Irms = Vrms/R = 24/24 = 1A P = Irms * Irms * R = 1 * 24 = 24W .................................................................................................................................................................................................................................. [3] A thyristor half wave controlled converter has a supply voltage of 240V at 50Hz and a load resistance of 100 Ohm. when the firing delay angle is 30 the average value of load current is A. 126A B. 2.4A C. 126mA D. 24 A Exp:We know the output wave form of the half wave rectifier For any delay angle alpha, the average load voltage is given by

solving,

substituting the values in the above equation, Vav = (√2*240) / (2π) * [ 1 + cos30 ] = 100.8 V Iav = Vav/R = 100.8/100 = 126 mA .................................................................................................................................................................................................................................. [4] A full-wave fully controlled bridge has a highly inductive load with a resistance of 55 Ohm, and a supply of 110V at 50Hz. The value of load power for a firing angle α=75° is A. 10W B. 11W C. 10.5W


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P.M.MEVADA D. 10.9W Exp: Vav = [2Vm/(π)]cosα] = [(2 *√(2*110)/ 3.14 ] * cos 75 = 99 cos 75 = 25.6V Iav = Vav / R = 25.6/55 = 0.446A = Irms P = Irms * Irms * R = 0.446 * 0.446 * 55 =10.9W .................................................................................................................................................................................................................................. [5] A D.C. to D.C. chopper operates from a 48 V source with a resistive load of 24Ohm. The chopper frequency is 250Hz. When Ton= 3 ms, the rms current is A. 1.5A B. 15mA C. 1.73A D. 173mA Exp: Vav = V *f * Ton = 48 * 250 * 3 *(10 - 3) = 36V Iav = Vav/R = 36/24 = 1.5 A Vrms = V* Square root (Ton) * f = 48 * √0.75 = 41.6V Irms = Vrms/R = 41.6/24 = 1.73A .................................................................................................................................................................................................................................. [6] A 240V, 50Hz supply feeds a highly inductive load of 50 Ohm resistance through a thyristor full control bridge. when the firing angle α= 45°, load power is A. 456 W B. 466 W C. 732 W D. 120 W Exp: Vav = (2Vm/π) * cosα = [(2 * 339)/3.14] cos 45 = 152.6V Iav = Vav/R = 152.6 / 50 = 3.05A = Irms P = Square of Irms * R = 3.04 * 3.04 * 50 = 466W .................................................................................................................................................................................................................................. [7] Thermal runaway is not possible in FET because as the temperature of FET increases A. The mobility decreases B. The transconductance increases C. The drain current increases D. None of the above [8] The ripple frequency from a full wave rectifier is A. twice that from a half wave circuit B. the same as that from a half wave circuit C. half that from a half wave circuit D. 1/4 that from a half wave circuit [9] In a full-wave rectifier using two ideal diodes,Vdc & Vm are the dc & peak values of the voltage respectively across a resistive loaD. If PIV is the peak inverse voltage of the diode,then the appropriate relationships for the rectifier is A. Vdc=Vm/π,PIV=2Vm B. Vdc=2Vm/π,PIV=2Vm C. Vdc=2Vm/π,PIV=Vm D. Vdc=Vm/π,PIV=Vm [10] The output of a rectifier circuit without filter is


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P.M.MEVADA A. 50 Hz AC B. smooth DC C. pulsating DC D. 60 hz AC [11] An advantage of full wave bridge rectification is A. it uses the whole transformer secondary for the entire ac input cycle B. it costs less than other rectifier types C. it cuts off half of the ac wave cycle D. it never needs a filter [12] The best rectifier circuit for the power supply designed to provide high power at low voltage is A. half wave arrangement B. full wave, center tap arrangement C. quarter wave arrangement D. voltage doubler arrangement [13] If a half wave rectifier is used with 165Vpk AC input, the effective dc output voltage is A. considerably less than 165V B. slightly less than 165V C. exactly 165V D. slightly more than 165V [14] If a full wave bridge circuit is used with a transformer whose secondary provides 50Vrms, the peak voltage that occurs across the diodes in the reverse direction is approximately A. 50 Vpk B. 70 Vpk C. 100 Vpk D. 140 Vpk [15] The main disadvantage of voltage doubler power supply circuit is A. Excessive current B. Excessive voltage C. Insufficient rectification D. Poor regulation under heavy loads [16] A source follower using an FET usually has a voltage gain which is A. Greater than +100 B. Slightly less than unity but positive C. Exactly unity but negative D. About -10 [17] The average output voltage(Vdc) of the full wave diode bridge rectifier is A. Vm/2 B. 2Vm/pi C. 3Vm/pi D. 4Vm/pi [18] The typical ratio of latching current to holding current in a 20A thyristor is [GATE -2011] A. 5.0 B. 2.0 C. 1.0 D. 0.5 [19] A half controlled single phase bridge rectifier is supplying an R-L loaD. It is operated at a firing angle (alpha) and load current is continuous. The fraction of cycle that the freewheeling diode conducts is [GATE 2011]

Ans: D


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P.M.MEVADA Common Data for Questions [20] & [21] In the 3 phase inverter circuit shown, the load is balanced and the gating scheme is 180 degree conduction mode. All the switching devices are ideal , Vd = 300V

[20] The rms value of load phase voltage is [GATE -2011] A. 106.1V B. 141.4 V C. 212.2 V D. 282.8V HINT:- VL = Square root(2/3) * Vs [21] If the dc bus voltage Vd = 300v, the power consumed by 3 phase load is [GATE -2011] A. 1.5kW B. 2.0 kW C. 2.5 kW D. 3.0 kW HINT:- P = 3 * [(Vph * Vph)/Rph] Common Data for Question 22 & 23: 1 Pulse Transformer (PT) is used to trigger the SCR in the adjacent figure. The SCR is rated at 1.5KV, 250A with IL=250mA, IH=150mA, and IGmax= 150mA, IGmin=100mA. The SCR is connected to an inductive load, where L=150mH in series with a small resistance and the supply voltage is 200V dC. The forward drops of all transistors/ diodes and gate- cathode junction during ON state are 1.0V.

[22] The resistance R should be (a) 4.7K Ohm (b) 470 Ohm (c) 47 Ohm (d) 4.7 Ohm [23] The minimum approximate volt-second rating of the pulse transformer suitable for triggering the SCR should be: ( volt-second rating is the maximum of product of the voltage and the width of the pulse that may be applied (a) 2000 uV-s (b) 200 uV-s


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P.M.MEVADA (c) 20 uV-s (d) 2.0 uV-s [24] " Six MOSFETs connected in a bridge configuration (having no other power device) MUST be operated as a Voltage Source Inverter (VSI) ". This statement is [GATE-2007] A. True, because being majority carrier devices, MOSFETs are voltage driven B. True, because MOSFETs have inherently anti parallel diodes C. False, because it can be operated both as current source Inverter (CSI) or a VSI D. False, because MOSFETs can be operated as excellent constant current sources in the saturation region [25] A single phase full - wave half controlled bridge converter feeds an inductive loaD. The two SCRs in the converter are connected to a common DC bus. The converter has to have a free wheeling diode [GATE2007] A. because the converter inherently does not provide for free wheeling B. Because the converter does not provide for freewheeling for high values of triggering angles C. Or else the freewheeling action of the converter will cause shorting of the AC supply D. Or else if a gate pulse to one of the SCRs is missed, it will subsequently cause a high load current in the other SCR [26] The power electronic converter shown in the figure has a single pole double throw switch. the pole P of the switch is connected alternately to throws A and B. The converter shown is a [GATE-2010]

A. Step down chopper( buck converter) B. Half- wave rectifier C. Step Up chopper ( boost converter) D. full wave converter [27] Figure shows a composite switch consisting of a power transistor (BJT) in series with a diode. Assuming that the transistor switch and the diode are ideal, the I-V characteristic of the composite switch is [GATE2010]

Ans: C


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P.M.MEVADA [28] The fully controlled thyristor converter in the figure is fed from a single-phase source. When the firing angle is 0°, the dc output voltage of the converter is 300 V. What will be the output voltage for a firing angle of 60°, assuming continuous conduction? [GATE-2010]

(A) 150V (B) 210V (C) 300V (D) 100.(pi).V [29] The manufacturer of a selected diode gives the rate of fall of the diode current di/dt = 20 A/ms, and a reverse recovery time of trr =5 ms. What is value of peak reverse current? Ans: 44.72A HINT:-The peak reverse current is given as:

The storage charge QRR is calculated as Qrr = (1/2)*(di/dt)* SQU.(trr) = 1/2 X 20A/uS X 5u X 5u = 50uC. substitute the Qrr value in Irr equation.

[30] A three phase current source inverter used for the speed control of an induction motor is to be realized using MOSFET switches as shown below. Switches S1 to S6 are identical switches [GATE2011]


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P.M.MEVADA The proper configuration for realizing switches S1 to S6 is

Ans: C [31] Circuit turn-off time of an SCR is defined as the time [GATE2011] A. taken by the SCR to turn off B.required for SCR current to become zero C. for which the SCR is reverse biased by the commutation circuit D. for which the SCR is reverse biased to reduce its current below the holding current [32] A single phase fully controlled thyristor bridge ac-dc converter is operating at a firing angle of 25 degree, and an overlap angle 10 degree with constant dc output current of 20A. The fundamental power factor ( displacement factor) at input ac mains is [GATE2007] A. 0.78 B. 0.827 C. 0.866 D. 0.9 [33] A three phase fully controlled thyristor bridge converter is used as line commutated inverter to feed 50 KW power at 420 V DC to a three phase 415V(line), 50Hz as mains. Consider Dc link current to be constant. The rms current of the thyristor is [GATE2007] A. 119.05A B. 79.37A C. 68.73A D. 39.68A [34]which of the following statements are true about VI characteristic of SCR? A. Holding current is more than Latching current B. SCR will trigger if the applied voltage exceeds forward break over voltage C. SCR can be triggered without gate current D. When the SCR is in reverse biased, small leakage current will flow Options: A. A, B and C B. All are true C. B, C, D D. C, D [35] which of the following statements are true about BJT? (i) It has more power handling capability than MOSFET (ii) Has higher switching speed than IGBT and MOSFET (iii) Has low on state conduction resistance (iv) Has second breakdown voltage problem Options: A. All are true B. (i), (ii), (iii) and (iv) C. (i), (iii) and (iv) D. (ii), (iii) and (iv) [36] For a JFET, when VDS is increased beyond the pinch off voltage, the drain current A. Increases B. Decreases


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P.M.MEVADA C. Remains constant D. First decreases and then increases [37] n-channel FETs are superior to P-channel FETs, because A. They have higher input impedance B. They have high switching time C. They consume less power D. Mobility of electrons is greater than that of holes [38] Which of the following is true about the diodes A. During forward biased small amount of voltage drop will appear across anode and cathode B. If the reverse voltage exceed VRRM the diode will destroy C. trr is depends on softness factor D. schottky diodes have low trr Options: (i) All are true (ii) A, B, D (iii) A, B,C (iv) B,C, D The feature of schottky diode is low forward voltage drop, not low trr. [39] The MOSFET has (i)Higher Power handling capability than BJT (ii) Faster switching speed than BJT (iii) High on state resistance (iv) Secondary breakdown voltage problem which of the above statements are incorrect? Options: A. (i), (iii), (iv) B. (ii), (iii) C. All of the above D. (ii), (iii), (iv) [40] Which of the following is called as uncontrolled semiconductor device? A. Diode B. Thyristor C. GTO D. MOSFET [41] Which of the following is a half controlled semiconductor device? A. MOSFET B. GTO C. MCT D. SCR HINT:-In SCR only turn on of the device an be controllable by the gate signal. [42]Which of the following abbreviation is not a power semiconductor device? A. SIT B. SITH C. MCT D. IGCT Options: 1. a and d 2. a only 3. a, b, d 4. All are power semiconductor device HINT:- SIT – Static Induction Transistor SITH – Static Induction Thyristor MCT - MOS Controlled Thyristor IGCT – Integrated Gate Commutated Thyristor


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P.M.MEVADA [43] Which of the following statements are correct? A. IGBT is current driven device B. IGCT is voltage driven device C. MOSFET is voltage driven device D. GTO is minority carrier device Options: 1. a, b, c 2. b, c, d 3. All are correct 4. None are correct [44] The breakdown mechanism in a lightly doped p-n junction under reverse biased condition is called A. avalanche breakdown B. zener breakdown C. breakdown by tunnelling D. high voltage breakdown [45] For a large values of |VDS|, a FET behave as A. Voltage controlled resistor B. Current controlled current source C. Voltage controlled current source D. Current controlled resistor [46] In a full wave rectifier without filter, the ripple factor is A. 0.482 B. 1.21 C. 1.79 D. 2.05 [47] Space charge region around a P-N junction A. does not contain mobile carries B. contains both free electrons and holes C. contains one type of mobile carriers depending on the level of doping of the P or N regions D. contains electrons only as free carriers [48] In a JFET, at pinch-off voltage applied on the gate A. The drain current becomes almost zero B. The drain current begins to decrease C. The drain current is almost at saturation value D. The drain to source voltage is close to zero volts [49] The value of ripple factor of a half wave rectifier without filter is approximately A. 1.2 B. o.2 C. 2.2 D. 2.0 [50] In an intrinsic semiconductor, the Fermi-level is A. closer to the valence band B. midway between conduction and valence band C. closer to the conduction band D. within the valence band [51] The transformer utilization factor of a half wave rectifier is approximately A. 0.6 B. 0.3 C. 0.9


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P.M.MEVADA D. 1.1 [52] Transistor is a A. Current controlled current device B. Current controlled voltage device C. Voltage controlled current device D. Voltage controlled voltage device HINT:- For ex, the output current Ic depends on the input current Ib [53] If the output voltage of a bridge rectifier is 100V, the PIV of diode will be A. 100 * Square root(2) V B. 200/(pi) V C. 100 * (pi) V D. 100/2 V HINT:-Peak inverse voltage = max secondary voltage = Vdc= 2Vm/pi = 100 Vm = 100 * pi/2 [54] A 240V, 50Hz supply feeds a highly inductive load of 50 Ohm resistance through a half controlled thyristor bridge. When the firing angle α=45°, the load power is A. 418 W B. 512 W C. 367 W D. 128 W Exp: Vav = (Vm/π) (1 + cosα) = [(√2*240)/(π) ) ( 1 + cos45)] = 184.4 V Iav = Vav / R = 184.4/50 =3.69A

= 3.69 * √[(180 -45)/180] = 3.2A P = 3.2 * 3.2 *50 = 512 W ........................................................................................................................................ [55] A D.C. to D.C. chopper operates from a 48 V battery source into a resistive load of 24Ohm. The frequency of the chopper is set to 250Hz. When chopper on-time is 1 ms the load power is A. 6W B. 12W C. 24W D. 48W Exp: Vavg = V* f * Ton = 48 x 250 x (10 - 3) = 12V Iav = Vav/R = 12/24 = 0.5A Vrms= V* Square root (Ton) * f = 48 * Square root (0.25) = 24V Irms = Vrms/R = 24/24 = 1A P = Irms * Irms * R = 1 * 24 = 24W .............................................................................................................................. [56] A thyristor half wave controlled converter has a supply voltage of 240V at 50Hz and a load resistance of 100 Ohm. when the firing delay angle is 30 the average value of load current is A. 126A B. 2.4A C. 126mA D. 24 A Exp:We know the output wave form of the half wave rectifier For any delay angle alpha, the average load voltage is given by


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solving,

substituting the values in the above equation, Vav = (√2*240) / (2π) * [ 1 + cos30 ] = 100.8 V Iav = Vav/R = 100.8/100 = 126 mA .................................................................................................................................... [57] A full-wave fully controlled bridge has a highly inductive load with a resistance of 55 Ohm, and a supply of 110V at 50Hz. The value of load power for a firing angle α=75° is A. 10W B. 11W C. 10.5W D. 10.9W Exp: Vav = [2Vm/(π)]cosα] = [(2 *√(2*110)/ 3.14 ] * cos 75 = 99 cos 75 = 25.6V Iav = Vav / R = 25.6/55 = 0.446A = Irms P = Irms * Irms * R = 0.446 * 0.446 * 55 =10.9W ................................................................................................................................... [58] A D.C. to D.C. chopper operates from a 48 V source with a resistive load of 24Ohm. The chopper frequency is 250Hz. When Ton= 3 ms, the rms current is A. 1.5A B. 15mA C. 1.73A D. 173mA Exp: Vav = V *f * Ton = 48 * 250 * 3 *(10 - 3) = 36V Iav = Vav/R = 36/24 = 1.5 A Vrms = V* Square root (Ton) * f = 48 * √0.75 = 41.6V Irms = Vrms/R = 41.6/24 = 1.73A ....................................................................................................................................... [59] A 240V, 50Hz supply feeds a highly inductive load of 50 Ohm resistance through a thyristor full control bridge. when the firing angle α= 45°, load power is A. 456 W B. 466 W C. 732 W D. 120 W Exp: Vav = (2Vm/π) * cosα = [(2 * 339)/3.14] cos 45 = 152.6V Iav = Vav/R = 152.6 / 50 = 3.05A = Irms P = Square of Irms * R = 3.04 * 3.04 * 50 = 466W [60] The reverse recovery time of the diode is defined as the time between the instant diode current becomes zero and the instant reverse recovery current decays to A. Zero B. 10% of the reverse peak current (IRM)


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P.M.MEVADA C. 25% of (IRM) D. 15% of (IRM) [61] The cut-in voltage and forward-voltage drop of the diode are respectively A. 0.7V, 0.7V B. 0.7V, 1V C. 0.7V, 0.6V D. 1V, 0.7V [62] The softness factor for soft-recovery and fast-recovery diodes are respectively A. 1, >1 B. <1, 1 C. 1, 1 D. 1, <1 [63] Reverse recovery current in a diode depends on A. Forward field current B. Storage charge C. Temperature D. PIV [64] The three terminals of power MOSFET A. Collector, Emitter, base B. Drain, source, base C. Drain, source, gate D. Collector, emitter, gate [65]The three terminals of IGBT A. Collector, emitter, base B. Drain, source, base C. Drain, source, gate D. Collector, emitter, gate [66] The three terminals of MCT A. Anode, cathode, gate B. Collector, emitter, gate C. Drain, source, base D. Drain, source, gate [67] Compared to Power MOSFET, the Power BJT has A. Lower switching losses but higher conduction loss B. Higher switching losses and higher conduction loss C. Higher switching losses but lower conduction loss D. Lower switching losses and lower conduction loss [68] Which one of the following statement is true A. MOSFET has positive temperature coefficient whereas BJT has negative temperature Coefficient B. Both MOSFET and BJT have positive temperature coefficient C. Both MOSFET and BJT have negative temperature coefficient D. MOSFET has negative temperature coefficient whereas BJT has positive temperature coefficient [69] Which one of the following statement is true? A. Both MOSFET and BJT are voltage controlled devices B. Both MOSFET and BJT are current controlled devices C. MOSFET is a voltage controlled device and BJT is current controlled device


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P.M.MEVADA D. MOSFET is a current controlled device and BJT is voltage controlled device HINT:-MOSFET operation is controlled by gate voltage and the BJT operation is controlled by base current HINT for Questions 5, 6, 7:

MOSFET

IGBT

MCT

[70]An SCR is considered to be a semi-controlled device because [GATE 2009] A. It can be turned OFF but not ON with a gate pule B. It conducts only during one half-cycle of an alternating current wave C. It can be turned ON but not OFF with a gate pulse D. It can be turned ON only during one half-cycle of an alternating voltage wave [71] The current Source Inverter shown in figure is operated by alternatively turning on thyristor pairs(T1,T2) and (T3,T4). If the load is purely resistive, the theoretical maximum output frequency obtainable will be [GATE]

A. 125kHz B. 250kHz C. 500kHz D. 50kHz [72] In the chopper circuit shown, the main thyristor(TM) is operated at a duty ratio of 0.8 which is much larger the communication interval. If the maximum allowable reapplied dv/dt on TM is 50V/μs,what should be the theoretical minimum value of C1? Assume current ripple through L0 to be negligible. [GATE]


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A. 0.2μF B. 0.02μF C. 2μF D. 20μF [73] Match the switch arrangements on the top row to the steady-state V-I characteristics on the lower row.The steady state operating points are shown by large black dots. [GATE]

A. A-I, B-II, C-III, D-IV B. A-II, B-IV, C-I, D-III C. A-I, B-II, C-III, D-II D. A-IV, B-III, C-II, D-I [74] " Six MOSFETs connected in a bridge configuration (having no other power device) MUST be operated as a Voltage Source Inverter (VSI) ". This statement is [GATE 2007] A. True, because being majority carrier devices, MOSFETs are voltage driven B. True, because MOSFETs have inherently anti parallel diodes C. False, because it can be operated both as current source Inverter (CSI) or a VSI D. False, because MOSFETs can be operated as excellent constant current sources in the saturation region [75] A single phase full - wave half controlled bridge converter feeds an inductive loaD. The two SCRs in the converter are connected to a common DC bus. The converter has to have a free wheeling diode [GATE 2007] A. Because the converter inherently does not provide for free wheeling B. Because the converter does not provide for free wheeling for high values of triggering angles C. Or else the free wheeling action of the converter will cause shorting of the AC supply D. Or else if a gate pulse to one of the SCRs is missed, it will subsequently cause a high load current in the other SCR [76] A single phase fully controlled thyristor bridge ac-dc converter is operating at a firing angle of 25 degree, and an overlap angle 10 degree with constant dc output current of 20A. The fundamental power factor ( displacement factor) at input ac mains is [GATE 2007] A. 0.78 B. 0.827 C. 0.866 D. 0.9


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P.M.MEVADA [77] A three phase fully controlled thyristor bridge converter is used as line commutated inverter to feed 50KW power at 420V DC to a three phase 415V(line), 50Hz as mains. Consider Dc link current to be constant. The rms current of the thyristor is [GATE 2007] A. 119.05A B. 79.37A C. 68.73A D. 39.68A Statement for Linked Answer Questions:78 & 79 [GATE2012] The transfer function of a compensator is given as GC(s)=[(s+a)/(s+b)] [78] GC(s) is a lead compensator if A. a=1,b=2 B. a=3,b=2 C. a=-3,b=-1 D. a=3,b=1 [79] The phase of the above lead compensator is maximum at A. √2 rad/s B. √3 rad/s C. √6 rad/s D. √1/3 rad/s [80] Which of the following statements are correct? 1. Thyristor is current driven device 2. GTO is current driven device 3. GTR is current driven device 4. SCR is a pulse triggered device A.1 and 2 B.1, 2, 3 C.All D.4 only [81] Which of the following statements are correct? 1.GTO is a pulse triggered device 2.MOSFET is uni-polar device 3.SCR is a bipolar device 4.Continuous gate signal is not required to maintain the SCR to be in ON state A. 1, 2, 4 only B. 1, 2 only C. 4 only D. All [82] Which of the following is not a fully controlled semiconductor device? A. MOSFET B. IGBT C. IGCT D. SCR HINT:-Only turn on of the SCR can be controlled whereas in other devices we can control both turn on and turn off [83] Which of the following is not associated with p-n junction A. junction capacitance B. charge storage capacitance C. depletion capacitance D. channel length modulation [84] In a p-n junction diode under reverse bias, the magnitude of electric field is maximum at A. the edge of the depletion region on the p-side B. the edge of the depletion region on the n-side C. the p-n junction D. the center of the depletion region on the n-side


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P.M.MEVADA [85] An n-channel JFET has IDSS=2mA, and Vp=-4V. Its transconductance gm=(in mA/V) for an applied gate to source voltage VGS=-2V is A. 0.25 B. 0.5 C. 0.75 D. 1 [86]The MOSFET switch in its on-state may be considered equivalent to A. resistor B. inductor C. capacitor D. battery [87] The effective channel length of a MOSFET in a saturation decreases with increase in A. gate voltage B. drain voltage C. source voltage D. body voltage [88] The early effect in a bipolar junction transistor is caused by A. Fast turn – on B. Fast turn – off C. Large collector - base reverse bias D. Large emmiter - base forward bias [89] MOSFET can be used as a A. Current controlled capacitor B. Voltage controlled capacitor C. Current controlled inductor D. Voltage controlled inductors


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CHAPTER-6. OP-AMP [1]. A non inverting closed loop op amp circuit generally has a gain factor A. Less than one B. Greater than one C. Of zero D. Equal to one HINT: - For non inverting amplifier the gain is A = [1 + (Rf/Rin)]. So it will be always more than one [2]. If ground is applied to the (+) terminal of an inverting op-amp, the (–) terminal will A. Not need an input resistor B. Be virtual ground C. Have high reverse current D. Not invert the signal HINT: - Other options are not suitable. Please refer the Goodrich Interview Post for understanding inverting amplifier and virtual ground. [3] The closed-loop voltage gain of an inverting amplifier equal to A. The ratio of the input resistance to feedback resistance B. The open-loop voltage gain C. The feedback resistance divided by the input resistance D. The input resistance [4]. When a number of stages are connected in parallel, the overall gain is the product of the individual stage gains A. True B. False [5]. An ideal OP-AMP is an ideal a) Current controlled Current source b) Current controlled voltage source c) Voltage controlled voltage source d) voltage controlled current source HINT: - The ideal Opamp output voltage is maintained constant. It is controlled by input current. [6]. The ideal OP-AMP has the following characteristics. a) Ri=∞ ,A=∞ ,R0=0 b) Ri=0 ,A=∞ ,R0=0 c) Ri=∞ ,A=∞ ,R0=∞ d) Ri=0 ,A=∞ ,R0=∞ HINT: - Please refer the golden rules of Opamp. [7].Calculate the cutoff frequency of a first-order low-pass filter for R1 = 2.5kΩ and C1 = 0.05Μf A. 1.273kHz B. 12.73kHz C. 127.3 kHz D. 127.3 Hz HINT: low pass filter cut off frequency f = 1/(2πRC) [8]. How many op-amps are required to implement this equation

A. 2 B. 3 C. 4 D. 1


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P.M.MEVADA HINT: - The output voltage of inverting amplifier is Vout = (-Rf/Rin)Vin. By keeping 3 inverting amplifier, we can get this equation. [9]. How many op-amps are required to implement this equation Vo = V1 A.4 B.3 C.2 D.1 HINT: - The voltage follower which has one opamp has the output of Vo = Vin [10]. An OPAMP has a slew rate of 5 V/μ S .The largest sine wave O/P voltage possible at a frequency of 1 MHZ is A. 10 volts B. 5 volts C. 5/ volts D. 5/2 volts HINT: - Slew rate is defined as the max. rate of change of output voltage. Its unit is V/μS. Time period = 1/f = 1/1MHz = 1μS V= Vm. sin(ωt) = Vm. sin(2πf.t) slew rate = dV/dt = d(Vm. sin(2πf.t)/ dt=Vm. 2πf. cost [11] Explain the amplifier operation of OP-AMP? The golden rules of OP-AMP are: 1. Vout = A. Delta Vin [ A = Gain, Delta Vin = V+ - V-] 2. V-- < Vout < V++ 3. Zout = 0 , Zin+ = Zin- = Infinity The opamp will work as inverting amplifier and non- inverting amplifier based on the supply applied to its terminals. Non Inverting Amplifier Inverting Amplifier

[12]Interrupted and Asked to derive the equation... Current i = (Vin-Vout) / (Rin+Rf) =( Vin - Vx)/Rin = (Vout - Vx)/Rf Vx = virtual ground =the node at inverting input terminal =0 [13] Explain how transistor acts as a switch? The areas of operation for a transistor switch are known as the Saturation Region and the Cut-off Region. This means then that we can ignore the operating Q-point biasing and voltage divider circuitry required for amplification, and use the transistor as a switch by driving it back and forth between its "fully-OFF" (cut-off) and "fully-ON" (saturation) regions as shown below.


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[14] Interrupted and asked what is virtual ground?Explained. then i = Vin/Rin - Vx/Rin = Vout/Rf- Vout/Rf Rearranging we will get the final equation. [15] Which of the following amplifier is used in a digital to analog converter? A. non inverter B. voltage follower C. summer D. difference amplifier [16] Differential amplifiers are used in A. instrumentation amplifiers B. voltage followers C. voltage regulators D. buffers [17] For an ideal op-amp, which of the following is true? A. The differential voltage across the input terminals is zero B. The current into the input terminals is zero C. The current from output terminal is zero D. The output resistance is zero [18] The two input terminals of an opamp are labeled as A. High and low B. Positive and negative C. Inverting and non inverting D. Differential ans non differential [19] When a step-input is given to an op-amp integrator, the output will be A. a ramp. B. a sinusoidal wave. C. a rectangular wave. D. a triangular wave with dc bias. [20] For an op-amp having differential gain Av and common-mode gain Ac the CMRR is given by A. Av + Ac


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P.M.MEVADA B. Av / Ac C. 1 + [Av / Ac] D. Ac / Av [21] Hysteresis is desirable in Schmitt-trigger, because A. energy is to be stored/discharged in parasitic capacitances. B. effects of temperature would be compensateD. C. devices in the circuit should be allowed time for saturation and desaturation. D. it would prevent noise from causing false triggering. [22] The output voltage Vo of the above circuit is A. -6V B. -5V C. -1.2V D. -0.2V [23] In the above circuit the current ix is A. 0.6A B. 0.5A C. 0.2A D. 1/12A

Circuit for questions 22 &23

[24] Op-amp circuits may be cascaded without changing their input output relationships A. True B. False [25] An ideal OP-AMP is an ideal A. Current controlled Current source B. Current controlled Voltage source C. Voltage controlled Voltage source D. Voltage controlled Current source [26] A 741-Type OP-AMP has a gain-bandwith product of 1MHz. A non-inverting amplifier using this opamp & having a voltage gain of 20db will exhibit -3db bandwidth of A. 50KHz B. 100KHz C. 1000/17KHz D. 1000/7.07KHz [27] An amplifier using an opamp with slew rate SR=1v/sec has a gain of 40dB.If this amplifier has to faithfully amplify sinusoidal signals from dc to 20KHz without introducing any slew-rate induced distortion, then the input signal level exceed A. 795mV


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P.M.MEVADA B. 395mV C. 795mV D. 39.5mV [28] The ideal OP-AMP has the following characteristics A. Ri=∞,A=∞,R0=0 B. Ri=0,A=∞,R0=0 C. Ri=∞,A=∞,R0=∞ D. Ri=0,A=∞,R0=∞ [29] The approximate input impedance of the opamp circuit which has Ri=10k, Rf=100k, RL=10k A. ∞ B. 120k C. 110k D. 10k [30] An opamp has a slew rate of 5V/ S. the largest sine wave o/p voltage possible at a frequency of 1MHz is A. 10 V B. 5 V C. 5V D. 5/2 V [31] Assume that the op-amp of the fig. is ideal. If Vi is a triangular wave, then V0 will be A. square wave B. Triangular wave C. Parabolic wave D. Sine wave [32] A differential amplifier is invariably used in the i/p stage of all op-amps. This is done basically to provide the op-amps with a very high A. CMMR B. bandwidth C. slew rate D. open-loop gain [33] A differential amplifier has a differential gain of 20,000. CMMR=80dB. The common mode gain is given by A. 2 B. 1 C. 1/2 D.0 [34] In the differential voltage gain & the common mode voltage gain of a differential amplifier are 48db & 2db respectively, then its common mode rejection ratio is A. 23dB B. 25dB C. 46dB D. 50dB


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CHAPTER-7. MEASUREMENTS & INSTRUMENTATION [1] The major advantage of electromagnet type meter over a permanent magnet meter is A. The electromagnet meter costs much less B. The permanent magnet meter has a more sluggish coil C. The electromagnet meter need not be aligned with the earth’s magnetic field D. The electromagnet meter is more rugged [2] A thermocouple A. Gets warm when dc flows through it B. Is a thin, straight, special wire C. Generates ac when heated D. Generates dc when exposed to visible light [3] If the readings of the two watt meters in the 2 watt meter method of power measurement are 4.5 kW and 3.5 kW respectively and the latter reading has been obtained after reversing the current coil of the watt meter. What will be the total power in kW? A. 1 B. 3.5 C. 4.5 D. 8 [4]The major advantage of an electrostatic meter is A. It can handle large currents B. It measures very small currents C. It can detect and indicate ac voltages as well as dc voltages D. It draws a large current from a power supply. [5] The change in the direction of a compass needle, when a current carrying wire is brought near, is called A. Electromagnetic deflection B. Electroscopic force C. Magnetic force D. Electrostatic force [6] Ammeter shunts are useful because A. They prevent overheating of the meter movement B. They make a meter more physically rugged C. They allow for measurement of large currents D. They increase meter sensitivity [7] Suppose a certain current in a galvanometer causes the compass needle to deflect by 20 degree, then this current is doubled while the polarity stays the same. The angle of the needle deflection will A. Reverse direction B. Stay the same C. Increase D. Decrease [8] The major advantage of FETVM over a conventional voltmeter is that FETVM A. Can withstand higher voltages safely B. Draws less current from the circuit under test C. Can measure lower voltages D. Is sensitive to ac voltage as well as to dc voltage [9] The attraction or repulsion between two electrically charged objects is called A. Electromagnetic deflection B. Electrostatic force C. Electroscopic force D. Magnetic force [10] A utility meter’s reading indicates A. Current B. Power C. Voltage D. Energy [11] When a signal of 10 mV at 75 MHz is to be measured then which of the following instrument can be used


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P.M.MEVADA a) VTVM b) Cathode ray oscilloscope c) Moving iron voltmeter d) Digital multimeter [12] The most useful transducer for displacement sensing with excellent sensitivity, linearity and resolution is? a) an incremental encoder b) an absolute encoder c) LVDT d) a strain gauge [13] When variable reluctance type tachometer has 150 teeth on the rotor & the counter records 13,500 pulses per second then the rotational speed will be? a) 4800 rpm b) 5400 rpm c) 6000 rpm d) 7200 rpm. [14] One of the following, which is not a transducer in the true sense, is ? a) Thermocouple b) Piezoelectric pick up c) Photo-Voltaic cell d) LCD [15] Choose the correct statement (a) Digital multimeters are built using current measuring elements, while analog multimeters are built using voltage measuring units (b) Digital multimeters are built using voltage measuring units, while analog multimeters are built using current measuring units (c) Both digital and analog multimeters are built using voltage measuring units (d) Both digital and analog multimeters are built using current measuring units [16] An oscilloscope cannot be used to indicate A. Frequency B. Peak signal voltage C. Energy D. Wave shape [17] In two watt meter method of power measurement, if one of the watt meter shows zero reading, then it can be concluded that A. Power factor is unity B. Power factor is zero C. Power factor is 0.5 lagging D. Power factor is 0.5 leading [18] voltmeters should generally have A. High internal resistance B. Low internal resistance C. The ability to withstand large currents D. The greatest possible sensitivity [19] To measure the applied power supply voltage to the electrical circuit, the voltmeter should be placed A. In series with the circuit that works from the supply B. Between the positive pole of the supply and the circuit working from the supply C. Between the negative pole of the supply and the circuit working from the supply D. In parallel with the circuit that works from the supply [20] Which will not normally cause a large error in an ohmmeter reading? A. A slight change in switchable internal resistance B. A small voltage between points under test C. A small change in the resistance to be measured D. A slight error in the range switch position [21] Which is not function of the fuse?


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P.M.MEVADA A. To ensure there is enough current available for and appliance to work right B. To make sure the current drawn by an appliance can not exceed a certain limit C. To limit the amount of power that a device can draw from the electrical circuit D. To make it impossible to use appliances that are too large for a given circuit [22] The utility meter’s motor speed depends directly on A. The number of watt hours being used at the time B. The number of ampere hours being used at the time C. The number of watts being used at the time D. The number of kilowatt hours being used at the time [23] A typical frequency counter A. Works by indirectly measuring voltage B. Is accurate to six digits or more C. Works by indirectly measuring current D. Has an analog readout [24] A VU meter is never used to get a general indication of A. Sound intensity B. Visible light intensity C. Power in an audio amplifier D. Decibels [25] An analog voltmeter has a sensitivity of 10k/volt. The galvanometer used in constructing the instrument will produce a full scale deflection when the current passed through it is[10] An analog voltmeter has a sensitivity of 10k (a) 10 mA (b) 20 mA (c) 50 mA (d) 100 μA [26] Two sinusoidal signals of the same frequency are displayed on a dual-trace oscilloscope. One complete cycle of each signal covers 6 cm of the horizontal scale and the starting point of the horizontal scale and the starting point of the two signals are separated by 0.5 cm. The phase difference between the two signals in degrees is (a) 30 (b) 45 (c) 60 (d) 90 [27] Transient signals can be observed using (a) Storage oscilloscope (b) Sampling oscilloscope (c) Wave analyzer (d) Spectrum analyzer [28] The trace on an oscilloscope continually moves to the right of the screen when (a) The sweep is triggereD. (b) The sweep period is larger than the signal perioD. (c) The sweep period is smaller than the signal perioD. (d) There is no weep. [29] In a dual trace oscilloscope, the display appears segmented when (a) low frequency signals are observed in Alternate mode (b) low frequency signals are observed in Chop mode (c) high frequency signals are observed in Alternate mode (d) high frequency signals are observed in Chop mode [30] The meter movement in an illumination meter directly measures A. Current B. Power C. Voltage D. Energy


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P.M.MEVADA [31] Consider the following statements: 1.The main shortcomings of diaphragms are that they are prone to shock vibrations. 2.Diaphragms have the advantages of high accuracy and good dynamic response 3.Selection of material for diaphragms mainly depends upon temperature range and chemical nature of fluid coming in contact with diaphragm during pressure measurement. Which of the above statements is/are correct? [IES2010] A. 1,2 and3 B. 2 and 3 only C. 1 only D. 1 and 2 only [32] If reflection coefficient for voltage be 0.6, the voltage standing wave ratio(VSWR) is [IES2010] A.0.66 B.4 C.1.5 D.2 [33] A resistance strain gage with gage factor (Sf) of 2 is bonded to a steel member,which is subjected to a strain of 1 x 10-6.The original resistance value of this strain gage is 120Ω.The change in resistance due to the applied strain is [IES2010] A.60Ω B.240 x 10-6 Ω C.240Ω D.60 x 10-6 Ω [34] Consider the following statements: [IES2010] Piezoelectric materials 1.Crystal can be shown as electrical equivalent circuit similar to an inductor and a capacitor(Tank circuit). 2.Quartz,Rochelle salt,tourmaline. 3.Used in voltage stabilizers. 4.This exhibits the reverse effect of electrostriction. Which of the above statements are correct? A.1,2 and 4 only B.1 and 2 only C.2 and 4 only D.1,2,3 and 4 [35]Consider the following units for the measurement of pressure directly: [IES2010] 1.Rolta meter 2.Bourdon tube 3.Planti meter 4.Vanes Of these, the pressure can be measured by A. 1 and 2 only B. 3 and 4 only C. 2 only D. 1,2,3 and 4 [36] The measurement of Hall coefficient of a semiconductor with one type of charge carrier gives the information about [IES2010] A. sign of charge carrier B. density of charge carrier C. both sign and density of charge carrier D. mass of the charge carrier [37] A piezoelectric crystal has a thickness of 2.5mm and a voltage sensitivity of 0.05Vm/N. The piezoelectric crystal is subjected to an external pressure of 1.6 x 106N/m2,then the corresponding output voltage is, [IES2010] A. 200V B. 3.2 x 109V/m of thickness


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P.M.MEVADA C. 0.07 x 10-9V/(m3/New) D. 200m V [38]The two inputs of a CRO are fed with two stationary periodic signals. In the X-Y mode, the screen shows a figure which changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. The following inference can be made from this. [GATE2009] A.The signals are not sinusoidal B. The amplitudes of the signals are very close but not equal C. The signals are sinusoidal with their frequencies very close but not equal D. There is a constant but small phase difference between the signals [39]The pressure coil of a dynamo meter type wattmeter is [GATE2009] A. Highly inductive B. Highly resistive C. Purely resistive D. Purely inductive [40]The measurement system shown in the figure uses three sub systems in cascade whose gains are specified as G1, G2 and 1/G3. The relative small errors associated with each respective subsystem G1, G2,G3 are ε1,ε2 and ε3.The error associated with the output is [GATE2009]

A.ε1+ε2+1/ε3 B.(ε1.ε2)ε3 C.ε1+ε2-ε3 D.ε1+ε2+ε3 [41] A hot-wire ammeter A. Can measure ac as well as dc B. Registers current changes very fast C. Can indicate very low voltages D. Measures electrical energy [42] The device used to indicate the presence of an electric current is A. Electrometer B. Galvanometer C. Voltmeter D. Coulometer [43] A watt-hour meter measures A. Voltage B. Current C. Energy D. Power [44] A voltmeter should have A. Low internal resistance B. High internal resistance C. Electrostatic plates D. A sensitive amplifier [45] An average-reading digital multimeter reads 10V when fed with a triangular wave, symmetric about the time-axis.For the same input an rms-reading meter will read [GATE] A. 20/√3 B. 10/√3 C. 20√3 D. 10√3 [46] The figure shows a three-phase delta connected load supplied from a 400V,50Hz,3-phase balanced source. The pressure coil(PC) and current coil(CC) of a wattmeter are connected to the load as shown,with the coil polarities suitably selected to ensure a positive deflection. The wattmeter reading will be [GATE]


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A. 0 B. 1600Watt C. 800Watt D. 400Watt [47] The probes of a non-isolated, two channel oscilloscope are clipped to points A,B and C in the circuit of the adjacent figure. Vin is a square wave of a suitable low frequency. The display on Ch1 and Ch2 are as shown on the right. Then the "signal" and "ground" probes S1, G1 and S2, G2 of Ch1 and Ch2 respectively are connected to points [GATE 2007]

A. A, B, C, A B. A, B, C, B C. C, B, A, B D. B, A, B, C [48] An analog voltmeter uses external multiplier settings. With a multiplier setting of 20kΩ, it reads 440V and-with a multiplier setting of 80kΩ it reads 352V. For a multiplier setting of 40kΩ,voltmeter reads [GATE2012] A. 371V B. 383V C. 394V D. 406V [49] The rate at which charge carriers flow is measured in A. Coulombs B. Amperes C. Watt-hour D. Watts [50] The main problem with bar-graph meters is that A. They are not very sensitive B. They are unstable C. They cannot give very precise readings D. They can display only peak values


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CHAPTER-8. BASIC ELECTRONICS ELECTRONIC DEVICES [1] A diode can be used as a frequency multiplier because of its A. Junction capacitance B. Non linearity C. Avalanche voltage D. Forward breakover E. Charge carrier concentration [2] Which of the following is not a common form of data transmission A. Polarization modulation B. Frequency modulation C. Amplitude modulation D. Phase modulation E. Pulse modulation [3] A very brief, high voltage spike on an ac power line is called as A. A bleeder B. An arc C. A transient D. An avalanche E. A clipped peak [4] Which of the following is not characteristic of an oscillator? A. Negative feedback B. Good output to input coupling C. Reasonably high transistor gain D. Alternating current signal output E. Usefulness as a signal generator [5] The other name for beta of BJT is A. Current amplification factor B. Voltage amplification factor C. Power amplification factor D. Maximum amplification frequency E. Optimum amplification frequency [6] You can find the zener diode in A. The mixer in a superheterodyne receiver B. The PLL in a circuit for detecting FM C. The product detector in a receiver for SSB D. The voltage regulator in a power supply E. The AF oscillator in an AFSK transmitter [7] When the bias in an FET stops the flow of current, the condition is called A. Forward breakover B. Cutoff C. Reverse bias D. Pinchoff E. Avalanche [8] The VA rating of a transformer is an expression of A. The maximum frequency at which it can function B. The type of core material it has C. The voltage step-up or step-down ratio D. The impedance transfer ratio E. None of the above [9] In N-type semiconductor, the minority carriers are A. Electrons B. Protons


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P.M.MEVADA C. Holes D. Positrons [10] A disadvantage of a half wave rectifier is the fact that A. The output voltage is excessive compared to that of a full-wave rectifier B. The output current is excessive compared to that of a full-wave rectifier. C. The output waveform is harder to filter than is the case with a full wave rectifier D. It requires several expensive diodes, whereas a full wave rectifier requires only a single diode [11] A power gain of 30dB is equivalent to which amplification factor? A. 0.001 B. 1/30 C. 30 D. 1000 E. None [12] A differential amplifier, amplifies a. and mathematically differentiates the average of the voltages on the two input lines b. and differentiates the input waveform on one line when the other line is grounded c. the difference of voltages between the two input lines d. and differentiates the sum of the two input waveform [13] The type of power amplifier which exhibits crossover distortion in its output is a. Class A b. Class B c. Class AB d. Class C [14] The lowest output impedance is obtained in case of BJT amplifiers for a. CB configuration b. CE configuration c. CC configuration d. CE with RE configuration [15] The upper cutoff frequency of an RC coupled amplifier mainly depends upon a. Coupling Capacitor b. Emitter bypass capacitor c. Output capacitance of signal source d. Inter-electrode capacitance and stray shunt capacitance [16] Just as a voltage amplifier amplifies signal voltage, a power amplifier a. amplifies power b. amplifies signal current c. merely converts the signal ac power into the dc power d. merely converts the dc power into useful ac power [17]An oscillator of the LC type that has a split capacitor in the circuit is a. Hartly oscillator b. Colpitts oscillator c. Weinbridge oscillator d. R-C phase shift oscillator [18] The function of bleeder resistor in a power supply is a. the same as that of load resistor b. to ensure a minimum current drain in the circuit c. to increase the output dc voltage d. to increase the output current [19] In a bistable multivibrator circuit, commutating capacitor is used a. to increase the base storage charge b. to provide ac coupling c. to increase the speed of response d. to provide the speed of oscillations [20] Removing bypass capacitor across the emitter-leg resistor in a CE amplifier causes (A) increase in current gain.


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P.M.MEVADA (B) decrease in current gain. (C) increase in voltage gain. (D)decrease in voltage gain. [21] Removing bypass capacitor across the emitter leg resistor in a CE amplifier causes a. increase in current gain b. decrease in current gain c. increase in voltage gain d. decrease in voltage gain [22] The minimum number of flip-flops required to construct a mod-75 counter is a. 5 b. 6 c. 7 d. 8 [23] The important characteristic of emitter-follower is a. High input impedance and high output impedance b. High input impedance and low output impedance c. Low input impedance and low output impedance d. Low input impedance and high output impedance [24] When an amplifier is provided with current series feedback, its a. Input impedance increases and output impedance decreases b. Input and output impedance both decrease c. Input impedance decreases and output impedance increases d. Input and output impedance both increase [25] The frequency of oscillation of a tunnel-collector oscillator having L= 30μH and C = 300pf is nearby a. 267 kHz b. 1677 kHz c. 1.68 kHz d. 2.67 kHz HINT: - fo = 1/[2(pi)*square root(LC)] [26] The control terminal (pin 5) of 555 timer IC is normally connected to ground through a capacitor (0.01μF). This is to a. Protect the IC from inadvertent application of high voltage b. Prevent false triggering by noise coupled onto the pin c. Convert the trigger input to sharp pulse by differentiation d. Suppress any negative triggering pulse [27] The fan out of a MOS logic gate is higher than that of TTL gates because of its a. Low input impedance b. high output impedance c. Low output impedance d. High input impedance [28] The common collector amplifier is also known as a. Collector follower b. Base follower c. Emitter follower d. Source follower [29] In class-A amplifier, the output current flows for a. A part of the cycle or the input signal b. The full cycle of the input signal c. Half the cycle of the input signal d. 3/4th of the cycle of the input signal [30] In an amplifier with negative feedback a. Only the gain of the amplifier is affected b. Only the gain and bandwidth of the amplifier are affected c. Only the input and output impedance are affected d. All of the four parameters mentioned above would be affected


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P.M.MEVADA [31] When the elements of an RLC circuit are both magnitude scaled and frequency scaled, which quality is unaffected? a. resistor b. resonant frequency c. bandwidth d. quality factor [32] What kind of filter can be used to select a signal of one particular radio station? a. low pass b. high pass c. band pass d. band stop [33] A voltage source supplied a signal of constant amplitude, from 0 to 40kHz, to an RC lowpass filter. The load resistor experiences the maximum voltage at a. dc b. 10 kHz c. 20 kHz d. 40 kHz [34] The most commonly used amplifier in sample & hold circuits is A. A unity gain non-inverting amplifier B. A unity gain inverting amplifier C. An inverting amplifier with a gain of 10 D. An inverting amplifier with a gain of 100 [35] Three identical amplifiers with each one having a voltage gain of 50, input resistance of 1K & output resistance of 250,are cascaded. The open circuit voltage gain of combined amplifier is A. 49dB B. 51dB C. 98dB D. 102dB [36] The cascade amplifier is a multistage configuration of A. CC-CB B. CE-CB C. CB-CC D. CE-CC [37] The current gain of a BJT is A. gmr0 B. gm/r0 C. gmrπ D. gm/rπ [38] Introducing a resistor in the emitter of a common amplifier stabilizes the dc operating point against variations in A. Only the temperature B. Only the β of the transistor C. Both Temperature & β D. None of the above [39] Voltage Series feedback (also called series-shunt feedback) results in A. Increase in both input & output impedences B. Decrease in both input & output impedences C. Increase in input impedence & decrease in output impedence D. Decrease in input impedence & increase in output impedence [40] An amplifier without feedback has a voltage gain of a 50,input resistance of 1K & Output resistance of 2.5K. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback of 0.2 is A. 1/11K B. 1/5K C. 5K


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P.M.MEVADA D. 11K [41]Consider the parallel RLC circuit having R= 1, L= 1H, C=1F . What type of response will the circuit produce? a. Under damped b. Over damped c. Critically damped d. none of these [42] How much inductance is needed to resonate at 5 kHz with a capacitance of 12nF? a. 2652 H b. 11.844 H c. 3.333 H d. 84.33 mH [43] The difference between the half power frequencies is called the a. quality factor b. resonant frequency c. bandwidth d. cutoff frequency [44] A parallel RLC circuit has C=0.25F & L=2H. The value of R which will create unity damping factor is a. 1 b. 2 c. 0.5 d. 4 [45] A zero of the transfer function 10(s+1) H(s) = -----------is at (s+2)(s+3) a. 10 b. -1 c. -2 d. -3 [46] On the Bode magnitude plot, the slope of the pole 1/(5 + jω)2 is a. 20 dB/decade b. 40 dB/decade c. - 40 dB/decade d. -20 dB/decade [47] On the bode phase plot, the slope of [1 + j10ω - ω2/25]2 is a. 45°/decade b. 90°/decade c. 135°/decade d. 180°/decade [48] In an electric circuit, the dual of resistance is a. conductance b. capacitance c. open circuit d. inductance [49] In a series RLC circuit, which of these quality factors has the steepest curve at resonance? a. Q = 20 b. Q = 12 c. Q = 8 d. Q = 4 [50] In a parallel RLC circuit, the bandwidth B is directly proportional to R a. True b. False [51] Wien bridge oscillator can typically generate frequencies in the range of a. 1kHz - 1 Mhz


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P.M.MEVADA b. 1 Mhz - 10MHz c. 10MHz - 100MHz d. 100MHz - 150MHz [52] The barrier voltage present in a junction diode is the effect of A. The P side and N side of the junction forming a battery B. The emf required to move the holes fast enough to have the mobility equal to that of the electrons C. The recombination of charge carriers across the junction leaving behind the opposite charged ions D. The voltage needed to make the semiconductor material behave as a conductor [53] Compare to BJT the FET has A. High input impedance B. High gain bandwidth product C. Better current controlled behaviour D. High noise immunity [54] An intrinsic semiconductor at absolute zero temperature A. Has a large number of holes B. Behaves like an insulator C. Behaves like a metallic conductor D. Has few holes and same number of electrons [55] For the operation of a depletion type N-MOSFET, the gate voltage has to be A. Low positive B. High positive C. High negative D. Zero [56] An emitter follower has high input impedance because A. Large emitter resistance is used B. Large biasing resistance is used C. There is negative feedback in the base emitter circuit D. The emitter base junction is highly reverse biased [57] In a differential amplifier an ideal CMRR is A. Infinity B. Zero C. -1 D. +1 [58] In a PNP circuit, the collector A. Has a arrow pointing inward B. Is positive with respect to the emitter C. Is biased at a small fraction of the base bias D. Is negative with respect to the emitter [59] A PNP transistor can be replaced with an NPN device and the circuit will do the same thing, provided that A. The power supply or battery polarity is reversed B. The collector and emitter leads are interchanged C. The arrow is pointing inward D. A PNP transistor can never be replaced with NPN transistor [60] A BJT has A. Three PN junctions B. Three semiconductor layers C. Two N type layers around a P type layer D. A low avalanche voltage [61] The band gap of silicon at room temperature is________ A) 1.3 eV B) 0.7 eV C) 1.1 eV D) 1.4 eV


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P.M.MEVADA [62] The primary reason for the widespread use of Silicon in semiconductor device technology is A) Abundance of silicon on the surface of the earth B) Larger bandgap of silicon in comparison to germanium C) Favorable properties of silicon-dioxide (SiO2) D) Lower melting Point [63] The cascade amplifier is a multistage configuration of A) CC-CB B) CE-CB C) CB-CC D) CE-CC [64] In a multi-stage RC coupled amplifier the coupling capacitor______________ A) Limits the low frequency response B) Limits the high frequency response C) Does not affect the frequency response D) Block the DC component without affecting the frequency response [65] In forward mode npn BJT, if the voltage Vcc is increased then the collector current will increase A. Due to ohm's law, higher Vcc causes higher current B. Due to base width decrease less carrier recombine in the base region C. As the gradient of the minority carriers in the base region becomes steeper D. Due to both the B and C [66] A transistor is in active region whena) IB = βIC b) IC= βIB c) IC=IE d) IC=IB [67] In a JFET gates are always? a) forward biased b) reverse biased c) unbiased d) none [68] In schotty barrier diode current flows because of? a) Majority carriers b) Minority carriers c) Majority and minority carriers d) None [69] The early voltage of a BJT is VA = 75V. The minimum required collector current, such that the output resistance is at least r0 = 200kΩ, is (a) 1.67mA (b) 5mA (c) 0.375mA (d) 0.75mA [70] TVS diode is used for (a) Voltage protection (b) Current protection (c) ESD protection (d) None of the above [71] The amplifier is which current is proportional to the signal voltage, independent of source load resistance is called a)Current Amplifier b)Voltage Amplifier c)Transresistance amplifier d)Transconductance amplifier [72] Alternatively the characteristic impedance is called a)Surge Impedance


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P.M.MEVADA b)Match Impedance c)Alternative Impedance d)Reflected Impedance [73] In an RL circuit after a very long time of application of step voltage the inductance L is represented in its equivalent circuit as Incorrect! a)Open Circuit b)Short Circuit c)L / 2 d)2L [74] By passing a triangular wave through a differentiating circuit the output wave shape is a)Spikes b)Squarewave c)Sawtooth d)Sinewave [75] Clipper circuits are used to obtain any one of the following waveforms a)Sharper b)Rectified c)Fast Rising d)Smaller Amplitude [76] When a piece of copper and another of germanium are cooled from room temperature to 800 K then the resistance of a) Each of them increases b) Each of them decreases c) Copper increases and germanium decreases d) Copper decreases and germanium increases [77]When a sample of germanium and silicon having same impurity density are kept at room temperature then? a) Both will have equal value of resistivity b) Both will have equal value negative resistivity c) Resistivity of germanium will be higher than that of silicon d) Resistivity of silicon will be higher than that of germanium [78] When an RC driving point impedance function has zeros at s= -2 and s=-5 then the admissible poles for the function would be? a) s = 0; s = -6 b) s = 0; s = -3 c) s = 0; s = -1 d) s = -3; s = -4 [79] A transistor has CE parameter as hie = 10kW, hre=20 x 10-4 , hse = 100, hoe = 25 ms. The hib for this transistor will bea) 100 W b) 99.01 W c) 5m W d) 101kW [80] Which one of the following conditions for Z parameters would hold for a two port network containing linear bilateral passive circuit elements? a) Z11 = Z22 b) Z12Z21 = Z11Z22 c) Z11Z12 = Z22Z21 d) Z12 = Z21 [81] For harmonic generation the amplifier used is a)Audio Amplifier b)Class-A Amplifier c)RC Amplifier d)class-C Turned Amplifier


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P.M.MEVADA [82] Zener diodes semiconductors are a)Lightly Doped b)Heavily Doped c)Medium Doped d)Not at all Doped [83] In FET amplifiers, input is Incorrect! a)A current signal b)A voltage signal c)Either a current or voltage signal d)None of these [84] H-parameters of a transistor a)Are constant b)Vary with temperature c)Are dependent upon collector current d)None of these [85] In a voltage series feedback a)Output resistance increases while input resistance decreases b)Output and input resistances are reduced c)Output and input resistances are increased d)Output resistance decreases while input resistance increases [86]In a saturated transistor a)B-E junction is forward biased with C-B junction is reverse biased b)Both the junctions are forward biased c)B-E junction is reverse biased with C-B junction is forward biased d)Both the junctions are reverse biased [87]For an ideal noise free amplifier, the noise figure is a)Zero b)Zero dB c)Infinity d)1 dB [88]When a junction is formed between a metal and a semiconductor, the depletion layer is a)More on the side of the metal b)Equal on both sides c)Less on the side of the metal d)Less on semiconductor side [89] The impurity commonly used for realizing the base region of a silicon NPN transistor is ______ A) Gallium B) Indium C) Boron D) Phosphorus [90] A MOS capacitor made using P-type substrate is in the accumulation mode. The dominant charge in the channel is due to the presence of A) Holes B) Electrons C) Positively charged ions D) Negatively charged ions [91] A Zener diode works on the principle of ______ A) Tunneling of charge carriers across the junction B) Thermionic emission C) Diffusion of charge carriers across the junction D) Hopping of charge carriers across the junction [82] A BJT is said to be operating in the saturation region if______ A) Both the junctions are reverse biased B) Base-emitter junction is reverse biased & base-collector junction is forward biased


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P.M.MEVADA C) Base-emitter junction is forward biased & base-collector junction is reverse biased D) Both the junctions are forward biased [93] To obtain very high input & output impedances in a feedback amplifier, the topology used is A) Voltage-Series B) Current-Series C) Voltage-Shunt D) Current-Shunt [94] Cut off frequency of a bipolar transistor ____ A) Increase with the increase in base width B) Increase with the increase in emitter width C) Increase with the increase in the collector width D) Increase with the decrease in the base width [95] Negative feedback in amplifiers A) Improves the signal to noise ratio at the input B) Improves the signal to noise ratio at the output C) Does not affect the signal to noise ratio at the output D) Does not affect the signal to noise ratio at the input [96] The action of JFET in its equivalent circuit can be represented as a A. Current controlled Current source B. Current controlled Voltage source C. Voltage controlled Voltage source D. Voltage controlled Current source [97] A change in the value of the emitter resistance Re in a differential amplifier A. Affects the difference mode gain Ad B. Affects the common mode gain Ac C. Affects both Ad and Ac D. Does not effect either Ad and Ac [98] Generally, the gain of a transistor amplifier falls at high frequencies due to the A. Internal Capacitance of the device B. Coupling capacitor at the input C. Skin effect D. Coupling capacitor at the output [99] In a common emitter, unbypassed resistor provides A. Voltage shut feedback B. Current series feedback C. Negative voltage feedback D. Positive current feedback [100] A constant current signal across a parallel RLC circuits gives an o/p of 1.4V at the signal frequency of 3.89kHz. At the frequency of 4 kHz, the o/p voltage will be A. 1 V B. 2 V C. 1.4 V D. 2.8 V [101] Class AB operation is often used in power (large signal) amplifiers in order to A. Get maximum effeciency B. Remove even harmonics C. Overcome a crossover distortion D. Reducing collector dissipation [102] The bandwidth of an RF tuned amplifier is dependent on A. Q-factor of the tuned O/P circuit B. Q-factor of the tuned I/P circuit C. Quiescent operating point D. Q-factor of the O/P and I/P circuits as well as quiescent operating point [103]Most of the linear ICs are based on the two-transistor differential amplifier because of its A. Input voltage dependent linear transfer characteristics


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P.M.MEVADA B. High voltage gain C. High input resistance D. High CMMR [104] Negative feedback in an amplifier A. Reduces gain B. Increase frequency and phase distortion C. Reduces bandwidth D. Increase Noise [105] A dc power supply has no-load voltage of 30V and a full-load voltage of 25V at full-load current of 1A. Its output resistance and load regulation respectively are A. 5Ω & 20% B. 25Ω & 20% C. 5Ω &16.7% D. 25Ω & 16.7% [106] A Zener diode is used for a) Voltage Regulation b) Rectification c) Noise Suppression d) Blocking A.C [107] An SCR is a device having a) Three layers with four junctions b) Three layers with two junctions c) Four layers with three junctions d) Two layers with three junctions [108] An amplifier has a gain of 10,000 expressed in decibels the gain is a) 10 b) 40 c) 80 d) 100 [109] An emitter follows has a) High input impedance and high output impedance. b) High input impedance and low output impedance. c) Low input impedance and high output impedance. d) Low input impedance and low output impedance. [110] Semi-conductor diode time constant is equal to a) The value of majority carrier life time b) The life time of minority carrier c) The diffusion capacitance time constant d) Zero [111] To prepare a P type semiconducting material the impurities to be added to silicon are a) Boron, Gallium b) Arsenic, Antimony c) Gallium, Phosphorous d) Gallium, Arsenic [112] FET is a good signal chopper because a) It exhibits no offset voltage at zero drain current b) It occupies less space in integrated form c) It is less noisy d) It has got high input impedance [113] In Bipolar Junction transistors, the type of configuration which will give both voltage gain and current gain is a) CC b) CB c) CE d) None


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P.M.MEVADA [114] To increase the input resistance and decrease the output resistance in negative feedback, the type used is a) Voltage Shunt b) Current Series c) Voltage Series d) Current Shunt [115] A series capacitance used in a filter circuit represents a) Low-Pass b) Band-Pass c) High-Pass d) None [116] An ideal power supply is characterized by a) Very large output resistance b) Very small output resistance c) Zero internal resistance d) Infinite internal resistance [117] An ideal diode should have a) Zero resistance in the forward bias as well as reverse bias b) Zero resistance in the forward bias and an infinitely large resistance in reverse bias c) Infinitely large resistance in reverse bias d) Infinitely large resistance in forward as well as reverse bias [118] One coulomb-per-second is equal to one: a) watt b) joule c) volt d) ampere [119] Which of the following is one of the functions performed by a diode? a) filter b) amplifier c) rectifier d) inverter [120] What is the “power factor”? a) ratio of true power to apparent power b) peak power times 0.707 c) sin of the phase difference between E and I d) cos of the phase angle between true power and apparent power [121] In order for a BJT to conduct under the conditions of no signal input, the bias must be A. In the reverse direction at the E-B junction, sufficient to cause forward breakover. B. In the reverse direction at the E-B junction, but not sufficient to cause avalanche effect. C. Such that the application of a signal would cause the transistor to go into a state of cutoff. D. Such that the application of a signal would cause the transistor to go into a state of saturation. E. Such that the application of a signal would cause the transistor to become nonlinear. [122] The high input impedance of a MOSFET makes this type of device ideal for use in A. Weak-signal amplifiers B. High-power oscillators C. High-current rectifiers D. Antenna tuning networks E. Graphic equalizers [123] The drain of a JFET is the analog of the A. Plate of a vacuum tube B. Emitter of a BJT C. Cathode of diode D. Positive electrode in a solar cell E. Substrate of a MOSFET


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P.M.MEVADA [124] One of the technical limitations of capacitive proximity sensors is the fact that they A. Are not very sensitive to objects that are poor electrical conductors. B. Are insensitive to objects that reflect light. C. Are insensitive to metallic objects. D. Cannot be used with oscillators E. Require extreme voltages in order to function properly [125] The power factor in an ac circuit is defined as (a) The actual power divided by the maximum power the circuit can handle. (b) The ratio of the real power to the imaginary power. (c) The ratio of the apparent power to the true power. (d) The ratio of the true power to the apparent power. (e) The ratio of the imaginary power to the apparent power. [126] The amount of current that a silicon photodiode can deliver in direct sunlight depends on (a) The forward breakover voltage. (b) The thickness of the substrate. (c) The surface area of the P-N junction. (d) The applied voltage. (e) The reverse bias. [127] In an amplifier that employs a P-Channel JFET, the device can usually be replaced with an N-channel JFET having similar specifications, provided that (a). All the resistors are reversed in polarity for the circuit in question (b). The power supply polarity is reversed for the circuit in question (c). The drain, rather than the source, is placed at signal ground (d). The output is taken from the source, rather than from the drain. [128] Secondary breakdown occurs in (a). MOSFET but not in BJT (b). Both MOSFET and BJT (c). BJT but not in MOSFET (d). None of these [129] In a transistor (a). β = α/ (α +1) (b). β = α/ (1- α) (c). α = β/ (β-1) (d). α = (β+1)/β [130] In a multi-stage RC coupled amplifier the coupling capacitor______________ A) Limits the low frequency response B) Limits the high frequency response C) Does not affect the frequency response D) Block the DC component without affecting the frequency response

DIGITAL ELECTRONICS [1] It is required to construct a counter to count upto 100(decimal). The minimum number of flipflops required to construct the counter is A. 8 B. 7 C. 6 D. 5 [2] The gate that assumes the 1 state, if and only if the input does not take a 1 state is calleD........ A. AND gate B. NOT gate C. NOR gate D. Both b and c


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P.M.MEVADA [3] For NOR circuit SR flip flop the not allowed condition is.... A. S=0, R=0 B. S=0, R=1 C. S=1, R=1 D. S=1, R=0 HINT: - When S=R=1 the output is subject to unpredictable behaviour when S and R return to 0 simultaneously. [4] A bistable multivibrator is a A. Free running oscillator B. Triggered oscillator C. Saw tooth wave generator D. Crystal oscillator [5] For a large values of |VDS|, a FET behave as A. Voltage controlled resistor B. Current controlled current source C. Voltage controlled current source D. Current controlled resistor [6] When a step input is given to an op-amp integrator, the output will be A. a ramp B. a sinusoidal wave C. a rectangular wave D. a triangular wave with dc bias [7] In a full-wave rectifier without filter, the ripple factor is A. 0.482 B. 1.21 C. 1.79 D. 2.05 [8]Hysteresis is desirable in Schmitt-trigger, because A. Energy is to be stored/discharged in parasitic capacitance B. Effects of temperature would be compensated C. Devices in the circuit should be allowed time for saturation and desaturation D. It would prevent noise from causing false triggering [9] For a 10-bit DAC, the Resolution is defined by which of the following a) 1024 b) 1/1024 c) 10 d) None [10] SRAM full form is a) Serial Read Access Memory b) Static Random Access Memory c) Static Read-only Access memory [11] What are the minimum number of 2 to 1 multiplexers required to generate a 2 input AND gate and a 2 input Ex-OR gate? A) 1 and 2 B) 1 and 3 C) 1 and 1 D) 2 and 2


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P.M.MEVADA [12]The output of a logic gate is ‘1’ when all its inputs are at logic ‘0’. Then gate is either A) A NAND or an EX-OR gate B) A NOR or an EX-NOR gate C) An OR or a EX-NOR gate D) An AND or an Ex-OR gate [13] A PLA can be used A) As a microprocessor B) As a dynamic memory C) To realise a sequential logic D) To realise a combinational logic [14] A dynamic RAM consists of A) 6 Transistors B) 2 Transistors and 2 Capacitors C) 1 Transistor and 1 Capacitor D) 2 Capacitor only [15] When a CPU is interrupted, it A) Stops execution of instructions B) Acknowledges interrupt and branches of subroutine C) Acknowledges interrupt and continues D) Acknowledges interrupt and waits for the next instruction from the interrupting device.


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P.M.MEVADA

CHAPTER-9. CONTROL SYSTEM [1] An open loop system represented by the transfer function G(s) = (s-1) / (s+2)(s+3) is A. stable and of the minimum phase type B. stable and of the non-minimum phase type C. unstable and of the minimum phase type D. unstable and of the non-minimum phase type [2] The open loop transfer function G(s) of a unity feedback control system is given as, G(s) = [ k(s+2/3) / s2(s+2) ] From the root locus, it can be inferred that when k tends to positive infinity, A. three roots with nearly equal real parts exist on the left half of the s-plane B. one real root is found on the right half of the s-plane C. the root loci cross the jω axis for a finite value of k; k≠0 D. three real roots are found on the right half of the s-plane [3] Given that

then the value of A3 is [GATE2012] A. 15A+12I B. 19A+30I C. 17A+15I D. 17A+21I [4] The matrix [A]=

is decomposed into a product of a lower triangular matrix [L] and an upper triangular matrix [U]. The properly decomposed[L] and [U] matrices respectively are............The options A,B,C,D are given below.

A B C D Ans: none of the above [5] The input x(t) of a system are related as y(t) = ∫t-∞ x(τ)cos(3τ)dτ. The system is [GATE2012] A. time-invariant and stable B. stable and not time-invariant C. time-invariant and not stable D. not time-invariant and not stable [6]The feedback system shown below oscillates at 2 rad/s when [GATE2012]


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P.M.MEVADA A. k=2 and a=0.75 B. k=3 and a=0.75 C. k=4 and a=0.5 D. k=2 and a=0.5 [7] The Fourier transform of a signal h(t) is H(jω) = (2cosω)(sin2ω)/ω. The value of h(0) is [GATE2012] A. 1/4 B. 1/2 C. 1 D. 2 [8] The state variable description of an LTI system is given by

where y is the output and u is the input.The system is controllable for, [GATE2012] A. a1≠0,a2=0,a3≠0 B. a1=0,a2=0,a3≠0 C. a1=0,a2=0,a3=0 D. a1≠0,a2≠0,a3=0 [9] The state transition diagram for the logic circuit shown is [GATE2012]

Ans: D [10] Given that

then the value of A3 is [GATE2012] A. 15A+12I


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P.M.MEVADA B. 19A+30I C. 17A+15I D. 17A+21I [11] A system is described by the following state and output equations [dx1(t)/dt] =-3x1(t)+x2(t)+2u(t) [dx2(t)/dt]=-2x2(t)+u(t) y(t)=x1(t) where u(t) is the input and y(t) is the output The system transfer function is [GATE 2009] A. (s+2)/(s2+5s-6) B. (s+3)/(s2+5s+6) C. (2s+5)/(s2+5s+6) D. (2s-5)/(s2+5s-6) Ans: C [12] A two-port network is defined by the relation: [IES 2010] I=5V1+3V2 I2=2V1-7V2The value of Z12 is A. 3 B. -3 C. 3/41 D. 2/31 Ans: C [13] The Z-transform of x(K) is given by [IES 2010] x(Z)= {(1-e-T)z-1} / {(1-z-1)(1-e-Tz-1)} The initial value of x(0) is A. Zero B. 1 C. 2 D. 3 Ans: A [14] Consider the following statements with reference to the phase plane: 1. They are general and applicable to a system of any order. 2. Steady state accuracy and existence of limit cycle can be predicteD. 3. Amplitude and frequency of limit cycle if exists can be evaluateD. 4. Can be applied to discontinuous time system. Which of the above statements are correct? [IES2010] A. 1,2,3 and 4 B. 2 and 3 only C. 3 and 4 only D. 2,3 and 4 only Ans: B [15] For the circuit shown below, the natural frequencies at port 2 are given by s+2=0 and s+5=0,without knowing which refers to open-circuit and which to short-circuit. Then the impedences Z11 and Z22 are given respectively by [IES2010]


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P.M.MEVADA

A. K1{(s+5)/(s+2)}, K2{(s+2)/(s+5)} B. K1{(s+2)/(s+5)}, K2{(s+5)/(s+2)} C. K1{(s)/(s+2)}, K2{(s+2)/(s+5)} D. K1{(s+2)/(s+5)}, K2{(s+2)/(s+5)} Ans: C [16] Consider the following statements in connection with two-position controller: 1.If the controller has a 4% neutral zone,its positive error band will be 2% and negative error band will be 8%. 2.The neutral zone is also known as dead banD. 3.The controller action of a two-position controller is very similar to that of a pure on-off controller. 4.Air-conditioning system works essentially on a two-position control basis. Which of the above statements are correct? [IES2010] A. 1,2 and 3 only. B. 2,3 and 4 only. C. 2 and 4 only. D. 1,2,3 and 4 Ans:B [17] The polar plot of an open loop stable system is shown below. The closed loop system is [GATE 2009]

A.Always stable B.Marginally stable C.Unstable with one pole on the RH s-plane D.Unstable with two poles on the RH s-plane Ans:C [18] The open loop transfer function of a unity feedback system is given by G(s) =(e -0.1s)/s.The gain margin of this system is [GATE 2009] A. 11.95 dB B. 17.67 dB C. 21.33 dB D. 23.9 dB Ans: D


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P.M.MEVADA [19]The first two rows of Routh’s tabulation of a third order equation are as follows. s3 2 2 s2 4 4 This means there are [GATE 2009] A.Two roots at s =± j and one root in right half s-plane B.Two roots at s =± j2 and one root in left half s- plane C.Two roots at s = ±j2 and one root in right half s-plane D.Two roots at s =± j and one root in left half s-plane Ans:D [20]The asymptotic approximation of the log magnitude vs frequency plot of a system containing only real poles and zeros is shown. Its transfer function is [GATE 2009]

A.[10(s+5)]/[s(s+2)(s+25)] B.[1000(s+5)]/[s2(s+2)(s+25)] C.[100(s+5)]/[s(s+2)(s+25)] D.[80(s+5)]/[s2(s+2)(s+25)] Ans:B [21]The trace and determinant of a 2x2 matrix are known to be -2 and -35 respectively. Its eigen values are [GATE 2009] A.-30 and -5 B.-37 and -1 C.-7 and 5 D.17.5 and -2 Ans:C [22]A Linear Time Invariant system with an impulse response h(t) produces output y(t) when input x(t) is applied. When the input x(t-τ) is applied to a system with impulse response h(t-τ), the output will be [GATE 2009] A.y(t) B.y(2(t-τ)) C.y(t-τ) D.y(t-2τ) Ans:D [23]For the Y-bus matrix of a 4-bus system given in per unit, the buses having shunt elements are [GATE 2009]


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P.M.MEVADA A. 3 and 4 B. 2 and 3 C. 1 and 2 D. 1,2 and 4 Ans:C [24]The unit step response of a unity feedback system with open loop transfer function G(s) = K / ((s+1)(s +2)) is shown in the figure. The value of K is [GATE 2009]

A. 0.5 B. 2 C. 4 D. 6 Ans: D [25] For the driving point impedance function, Z(s)=[as2+7s+3]/[s2+3s+b], the circuit realization is shown below. The values of 'a' and 'b' respectively are [IES2010] A. 4 and 5 B. 2 and 5 C. 2 and 1 D. 2 and 3 Ans: C [26] For the following driving point impedance functions, which of the following statements is true? [IES2010] Z1(s)=(s+2)/(s2+3s+5) Z2(s)=(s+2)/(s2+5) Z3(s)=(s+2)/(s2+2s+1) Z4(s)=(s+2)(s+4)/(s+1)(s+3) A. Z1 is not positive real B. Z1 is positive real C. Z3 is positive real D. Z4 is positive real Ans: D [27] The steady state error of a unity feedback linear system for a unit step input is 0.1. The steady state error of the same system, for a pulse input r(t) having a magnitude of 10 and a duration of one second, as shown in the figure is [GATE2011]

A. 0 B. 0.1 C. 1


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P.M.MEVADA D. 10 Ans:A [28] A point z has been plotted in the complex plane, as shown in figure below [GATE2011]

The plot of the complex number y=1/z is...........The options A,B,C,D are given below.

A. B. C. D. Ans:D [29] The system represented by the input-output relationship y(t)= 5t∫-∞ x(τ)dτ, t>0 is A. Linear and casual B. Linear but not casual C. Casual but not linear D. Neither linear nor casual [30] For the system 2/(s+1), the approximate time taken for a step response to reach 98% of its final value is A. 1s B. 2s C. 4s D. 8s [33] Given the finite length input x[n] and the corresponding finite length output y[n] of an LTI system as shown below, the impulse response h[n] of the system is A.h[n]={1,0,0,1} B.h[n]={1,0,1} C.h[n]={1,1,1,1} D.h[n]={1,1,1} [34] The frequency response of G(s)=1/[s(s+1)(s+2)] plotted in the complex G(jω) plane (for 0< ω<∞) is....Options A, B, C, D are given below

A.

B.

C.

D.

Ans:A


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P.M.MEVADA [35] The system x=Ax+Bu with A=

B=

is A. stable and controllable B. stable but uncontrollable C. unstable but controllable D. unstable and uncontrollable [36] The characteristic equation of a closed-loop system is a(s+1)(s+3)+k(s+2)=0,k>0. Which of the following statements is true? A. Its roots are always real B. It cannot have a breakaway point in the range -1

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P.M.MEVADA

CHAPTER-10. ELECTRICAL CIRCUIT THEORY [1] The period of the signal x(t) = 8 sin (0.8πt + π /4) is [GATE 2010] A. 0.4πs B. 0.8πs C. 1.25s D. 2.5s [2] The switch in the circuit has been closed for a long time. It is opened at t=0. At t=0+,the current through the 1μF capacitor is [GATE 2010]

A. 0A B. 1A C. 1.25A D. 5A [3] The second harmonic component of the periodic waveform given in the figure has an amplitude of [GATE 2010]

A. 0 B. 1 C. 2/π D. √5 [4] As shown in the figure, a 1 resistance is connected across a source that has a load line v+i=100. The current through the resistance is [GATE 2010]

A. 25A B. 50A C. 100A D. 200A [5] If the 12Ω resistor draws a current of 1A as shown in the figure, the value of resistance R is [GATE 2010]

A. 4Ω B. 6Ω C. 8Ω D. 18Ω


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P.M.MEVADA [5] If the electrical circuit of figure (b) is an eqiuvalent of the coupled tank system of figure (a), then [GATE 2010]

A. A,B are resistances and C,D capacitances B. A,C are resistances and B,D capacitances C. A,B are capacitances and C,D resistances D. A,C are capacitances are and B,D resistances [7] The two-port network P shown in the figure has ports 1 and 2, denoted by terminals (a,b) and (c,d), respectively. It has an impedence matrix Z with parameters denoted by Z ij. A 1Ω resistor is connected in series with the network at port 1 as shown in the figure. The impedance matrix of the modified two-port network (shown as a dashed box) is [GATE 2010]

A B C D Ans:C [8] The Maxwell's bridge shown in the figure is at balance.The parameters of the inductive coil are [GATE 2010]

A. R=R2R3/R4, L=C4R2R3 B. L=R2R3/R4, R=C4R2R3 C. R=R4/R2R3, L=1(C4R2R3) D. L=R4/R2R3, R=1/(C4R2R3)


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P.M.MEVADA Statement:

The L-C circuit shown in the figure has an inductance L=1mH and a capacitance C=10μF [9]: The initial current through the inductor is zero, while the initial capacitor voltage is 100V. The switch is closed at t=0. The current i through the circuit is: [GATE 2010] A. 5cos(5x103t)A B. 5sin(104t)A C. 10cos(5x103t)A D. 10sin(104t)A [10]: The L-C circuit of statement is used to commutate a thyristor, which is initially carrying a current of 5A as shown in the figure below. The values and initial conditions of L and C are the same as in statement. The switch is closed at t=0. If the forward drop is negligible, the time taken for the device to turn off is [GATE 2010]

A. 52μs B. 156μs C. 312μs D. 26μs [11] The voltage applied to a circuit is 100√2 cos(100πt) volts and the circuit draws a current of 10√2sin(100πt +π/4) amperes. Taking the voltage as the reference phasor, the phasor representation of the current in amperes is [GATE 2011] A. 10√2∠- π/4 B. 10∠- π/4 C. 10∠+ π/4 D. 10√2∠+ π/4 [12] A reactance network in the Foster's I form has poles at ω=∞(infinity). The element in box-1 in the above network is [IES2010]


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P.M.MEVADA A. a capacitor B. an inductor C. a parallel LC circuit D. a series LC circuit Statement for Linked Answer Questions 12 and 13: [GATE 2009]

[12] For the circuit given above, the Thevinin's resistance across the terminals A and B is [GATE 2009] A. 0.5kΩ B. C. 1kΩ D. 0.11kΩ [13] For the circuit given above, the Thevenin's voltage across the terminals A and B is [GATE 2009] A. 1.25V B. 0.25V C. 1V D. 0.5V [14] For the circuit shown, find out the current flowing through the 2Ω resistance. Also identify the changes to be made to double the current through the 2Ω resistance. [GATE]

A. (5A;Put Vs=20V) B. (2A;Put Vs=8V) C. (5A;Put Vs=10A) D. (7A;Put Vs=12A) [15] The common emitter forward current gain of the transistor shown is 100. The transistor is operating in [GATE 2007]


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P.M.MEVADA A. Saturation Region B. Cutoff Region C. Reverse active region D. Forward active region [16] The three – terminal linear voltage regulator is connected to a 10 ohm load resistor as shown in the figure. If Vin is 10V, what is the power dissipated in the transistor [GATE 2007]

A. 0.6W B. 2.4W C. 4.2W D. 5.4W Carry Two Marks Each Statement for Linked Answer Questions:17 & 18 In the circuit shown, the three voltmeter readings are V1=220V, V2=122V, V3=136V

[17] The power factor of the load is [GATE2012] a. 0.45 b. 0.50 c. 0.55 d. 0.60 [18] If RL=5Ω, the approximate power consumption in the load is [GATE2012] a. 700W b. 750W c. 800W d. 850W Common Data Questions: 19&20 With 10V dc connected at port A in the linear nonreciprocal two-port network shown below,following were observed: (1)1Ω connected at port B draws a current of 3A (2) 2.5Ω connected at port B draws a current of 2A


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P.M.MEVADA [19] For the same network, with 6V dc connected at port A, 1Ω connected at port B draws 7/3 A. If 8V dc is connected to port A, the open circuit voltage at port B is [GATE2012] a. 6V b. 7V c. 8V d. 9V [20] With 10V dc connected at port A, the current drawn 7Ω connected at port B is [GATE2012] a. 3/7A b. 5/7A c. 1A d. 9/7A [21] A balanced RYB-sequence,Y-connected(Star Connected) source with VRN=100 volts is connected to a Δconnected (Delta connected) balanced load of (8+j6) ohms per phase.Then the phase current and line current values respectively,are[IES2010] A.10A;30A B.10√3A;30A C.10A;10A D.10√3A;10√3A [22] Assuming both the voltage sources are in phase, the value of R for which maximum power is transferred from circuit A to circuit B is [GATE2012]

a. 0.8Ω b. 1.4Ω c. 2Ω d. 2.8Ω [23] The voltage gain Av of the circuit shown below is [GATE2012]

a. |Av| ≈200 b. |Av|≈100 c. |Av|≈20 d. |Av|≈10


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P.M.MEVADA [24] If VA-VB=6V, then VC-VD is [GATE2012]

a. -5V b. 2V c. 3V d. 6V Solution Hint: As Va-Vb =6 => I = V/R = 6/2 = 3A entering current = leaving current [ KCL] so current from Vd to Vc is same as 3A convert the current source to voltage source V = IR =2 x 1 = 2V

Vd = Vc + 2V + (3x1)V = Vc + 5V Vc-Vd = -5V [25]The circuit shown is a [GATE2012]

a. Low pass filter with f3db=[1/(R1+R2)C] rad/s b.High pass filter with f3db=[1/(R1C)] rad/s c. Low pass filter with f3db=[1/(R1C)] rad/s d. High pass filter with f3db=[1/(R1+R2)C] rad/s [6] In the circuit shown, an ideal switch S operated at 100kHz with a duty ratio or 50%. Given thatΔic 1.6A peak-to-peak and I0 is 5A dc, the peak current in S is [GATE2012]


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P.M.MEVADA a. 6.6A b. 5.0A c. 5.8A d. 4.2A Solution Hint: Δic = 1.6A peak-to-peak The positive peak = Δic /2 The current flows through the switch has a peak of = Io + Δic /2 For your information...The current waveform is like this

The lowest point will be 5A....highest point will be 5+ 0.8 [27] The i-v characteristics of the diode in the circuit given below are i={ [ V- 0.7 /500]A, V > or = 0.7 V 0A, V< 0.7 V The current in the circuit is [GATE 2012]

a. 10 mA b. 9.3 mA c. 6.67 mA d. 6.2 mA Sol. Hint: we have to find v and then apply in ct. equ... KVL...10 = 1K * i + v 10 = 1000i +v = 1000(v-0.7/500) + v solve it ....v= 0.8... [8] In the following figure, C1 and C2 are ideal capacitors. C1 has been charged to 12V before the ideal switch S is closed at t=0. The current i(t) for all t is [GATE 2012]


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P.M.MEVADA a. Zero b. A step function c. An exponentially decaying function d. An impulse function Sol. Hint: If it is RC ckt...ie any Resistance in series with capacitor, it will be an exponentially decaying function....here no resistance...so charge instantly....ie impulse function... [9] The impedance looking into nodes 1 and 2 in the given circuit is [GATE 2012]

a. 50 Ω b. 100 Ω c. 5 KΩ d. 10.1 KΩ Ans:A Answer [10] In the circuit given below,the current through the inductor is [GATE 2012]

a. (2/1+j)A b. (-1/1+j)A c. (1/1+j)A d. 0A Sol Hint: consider top half of the circuit R & L are in parallel with ct. source....other end connected to low potential...ie GND... convert ct. to V source...:


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Electrical Objective Book

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