ELECTRONICS AND COMMUNICATIONS ENGINEERING Materials and Components - Section 1 1.
Diamond is a paramagnetic material. A. True B. False Answer: Option B Explanation: Diamond is diamagnetic.
2.
Which capacitor-store higher amount of energy? A. Air capacitor B. Paper capacitor C. Mica capacitor D. Plastic film capacitor Answer: Option C Explanation: Energy stored is proportional to capacitance and capacitance is proportional to permittivity.
3.
Above ferroelectric curie temperature, spontaneous polarization in ferroelectric materials becomes stronger. A. True B. False Answer: Option B Explanation: Spontaneous polarization vanishes above ferro-electric Curie temperature.
4.
In paramagnetic materials A. permanent magnetic dipoles exist but the interaction between neighboring dipoles is negligible B. permanent magnetic dipole do not exist C. permanent magnetic dipoles exist and the interaction between neighboring dipoles is very strong D. permanent magnetic dipole moment may or may not exist Answer: Option A Explanation: In paramagnetic materials interaction between neighboring dipoles is negligible.
5.
Assertion (A): Atomic number of sodium is 11. Reason (R): Sodium has a body centered cubic lattice. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option B Explanation: Atomic number is not dependent on lattice structure.
6.
The conductivity of intrinsic semiconductor is given by A. eni(μp - μn) B. eni(μp + μn) C. ni(μp + μn) D. ni(μpμn) Answer: Option B Explanation: For intrinsic semiconductor,
Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and electrons).
7.
The core of a coil has a length of 10 cm. The self inductance is 8 mH. If the core length is doubled, all other quantities remaining the same, the self inductance will be A. 32 mH B. 16 mH C. 8 mH D. 4 mH Answer: Option D Explanation: Inductance is inversely proportional to the core length.
8.
The minority carrier life time and diffusion constant in a semiconducting material are 100 μs and 100 cm2/s respectively. The diffusion length of carriers is A. 0.1 cm B. 0.01 cm C. 0.0141 cm D. 1 cm Answer: Option A Explanation: Diffusion length = sqrt(Carrier life time x Diffusion constant) = (100 x 10-6 x 100)0.5= 0.1 cm.
9.
Assertion (A): Electronic and Ionic polarization in a polyatomic gas are independent of temperature. Reason (R): The orientation polarization is independent of temperature. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option C Explanation: Orientation polarization is inversely proportional to temperature.
10.
Two materials having temperature coefficients of 0.004 and 0.0004 respectively are joined in series. The overall temperature coefficient is likely to be A. 0.08 B. 0.04 C. 0.001 D. 0.0001 Answer: Option C Explanation: The overall temperature coefficient will be less than 0.004 and more than 0.0004.
11.
The number of valence electrons in pentavalent impurity is A. 5 B. 4 C. 3 D. 1 Answer: Option A Explanation: Pentavalent means 5 valence electrons.
12.
If the diameter of a wire is doubled, its current carrying capacity becomes A. one-fourth B. half C. twice D. four times Answer: Option D Explanation: Current carrying capacity depends on area of cross-section.
The law J = σE, where J is current density, σ is electrical conductivity and E is field strength is A. Ohm's law B. Gauss law C. Ampere's law D. Biot-Savart law Answer: Option A Explanation: It is another form of Ohm's law. 13.
14.
Assertion (A): Silicon is less sensitive to changes in temperature than germanium. Reason (R): Cut in voltage in silicon is less than that in germanium. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option C Explanation: Cut in voltage of silicon is higher than that in germanium.
15.
Material which lack permanent magnetic dipoles are known as A. paramagnetic B. diamagnetic C. ferromagnetic D. ferrimagnetic Answer: Option B Explanation: Diamagnetic materials have no permanent magnetic diploes.
16.
A parallel plate capacitor has its length, width and separation doubled. It fringing effects are neglected, to keep the capacitance same, the dielectric constant must be A. halved B. kept the same C. doubled D. made 4 times Answer: Option A Explanation: . When dimensions are changed, A become four times and d becomes twice.
17.
Assertion (A): In imperfect capacitors, the current does not lead the applied ac voltage by 90°. Reason (R): When subjected to ac fields, the dielectric constant can be expressed as ∈'r - j∈"r. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: Imaginary part of ∈r gives rise to absorption of energy by the material from alternating field. Hence current does not lead the voltage by 90°.
18.
In atomic physics, a state with l = 0 is called p state. A. True B. False Answer: Option B
Explanation: The state with l = 0 is called s state.
19.
If a sample of germanium and a sample of silicon have the same impurity density and are kept at room temperature A. both will have equal value of resistivity B. both will have equal negative resistivity C. resistivity of germanium will be higher than that of silicon D. resistivity of silicon will be higher than that of germanium Answer: Option D Explanation: Resistivity of silicon is more than that of germanium.
20.
When an electric field E is applied to solid and liquid insulating materials, the internal field Ei acting at the location of atom is such that A. Ei = E B. Ei > E C. Ei < E D. Ei may be equal to or less than E Answer: Option B Explanation: The actual field seen by an atom is larger than applied field.
21.
Which element exhibits the property of inertia? A. Resistance B. Capacitance C. Inductance D. Both resistance and inductance Answer: Option C Explanation: Inductance opposes rise and decay of current. Hence it has the property of inertia.
22.
For a permanent magnetic material A. the residual induction and coercive field should be large B. the residual induction and coercive field should be small C. area of hysteresis loop should be small D. initial relative permeability should be high Answer: Option A Explanation: Materials suitable for permanent magnet have large hysteresis loop. Hence residual and coercive field are large.
23.
In a coaxial cable, braided copper is used for A. conductor B. C. dielectric D. Answer: Option B Explanation: Braided material is used for shield.
shield jacket
24.
The hysteresis phenomenon in ferromagnetic materials exists at all temperatures. A. True B. False Answer: Option B Explanation: Hysteresis phenomenon exists below ferromagnetic curie temperature.
25.
Assertion (A): Magnetic susceptibility of diamagnetic materials is much less than that of paramagnetic materials. Reason (R): For diamagnetic as well as paramagnetic materials, μ r is nearly equal to 1.
A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: Magnetic susceptibility = (μr - 1)H. For diamagnetic and paramagnetic materials magnetic susceptibility is very very small and μr = 1.
26.
The attraction between the nucleus and valence electron of copper atom is A. zero B. weak C. strong D. either zero or strong Answer: Option B Explanation: The valence electron, in copper atom, can be easily detached from nucleus.
27.
If the temperature of an extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then A. the majority carrier density is doubled B. the minority carrier density is doubled C. the minority carrier density becomes 4 times the original value D. both the majority and minority carrier densities double Answer: Option D Explanation: As the intrinsic carrier concentration is doubled, the concentration of both electrons and holes is doubled.
28.
There is no hysteresis phenomenon is any dielectric material. A. True B. False Answer: Option B Explanation: Hysteresis phenomenon exists in dielectic materials. The units of μ0 and μr are A. H/m for both B. H/m for μr and no units for μ0 C. H/m for μ0 and no units for μr D. Wb/m for μ0 and no units for μr Answer: Option C Explanation: μr is only a numeric. 29.
30.
In metals the valence electron wave functions are strongly perturbed by the presence of neighbouring atoms. A. True B. False Answer: Option A Explanation: In a metal valence electrons are shared by all atoms.
31.
For a paramagnetic material, susceptiblity increases with increasing temperature. A. True B. False Answer: Option B Explanation: Susceptibility ∝ .
32.
Hydrogen is used in A. large size transformers B. MCB C. large size generators D. circuit breakers Answer: Option C Explanation: Modem large size generators have hydrogen cooling.
33.
Assertion (A): Ferroelectric materials have spontaneous polarization.
Reason (R): Above curie temperature, ∈ = for ferro-electric materials. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option B Explanation: Both A and R are correct. Spontaneous polarization vanishes above ferroelectric curie temperature. If e is the charge of an electron, R is the radius of its orbit and ω is the angular velocity of electron, the magnetic dipole moment μ m of the orbit is |μm| = eωR2. A. True B. False Answer: Option B Explanation: 1 μm 1 = 0.5 eωr2. 34.
35.
If ∈r' and ∈r" are the real and imaginary parts of complex dielectric constant ∈r, and δ is the loss angle. Then A.
B. C. tan δ = ∈'∈" D. tan δ = 1 - ∈' Answer: Option B Explanation: If ∈r" = 0, δ = 0. 36.
Assertion (A): At a temperature of 1000 K, thermionic emission current is about 0.1 A/cm2 of surface. Reason (R): Thermionic emission current is given by Ith = SA0 T2 e-Ew/kT. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: If different values are substituted in the equation for I th the value of emission current comes out to be about 0.1 A/cm2.
37.
At room temperature, the current in intrinsic semiconductor is due to A. holes
B. electrons C. ions D. holes and electrons Answer: Option D Explanation: Both electrons and holes contribute to flow of current in semiconductors.
38.
Ferroelectric materials are those which A. cannot be polarized B. have a permanent polarization C. have e equal to zero D. have μp = 0 Answer: Option B Explanation: Ferroelectric materials have permanent polarization. Assertion (A): Power loss in a conductor of resistance P = I2R. Reason (R): When a conductor is carrying current with current density J as a result of applied field E, then heat developed/m3/ second = JE. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: Heat developed depends an power loss. 39.
Assertion (A): For Diamond, μr = 1 Reason (R): Diamond is a diamagnetic material. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: For diamagnetic materials μr = 1. 40.
41.
If n denotes principal quantum number, the angular quantum number l = 0, 1... (n - 1). A. True B. False Answer: Option A Explanation: Angular quantum number determines the angular momentum of electron. Assertion (A): In a perfect capacitor, the current density is given by ω ∈0E0∈'rcos(ωt+ 90°), where ∈r' is real part of dielectric constant. Reason (R): In a perfect capacitor, dielectric losses are zero. A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: If dielectric losses are zero, the current in capacitor leads the applied voltage by 90°. Also imaginary part of is ∈r is zero. 42.
43.
Assertion (A): For a solenoid having N turns, . Reason (R): For all magnetic materials, B increases linearly with I.
A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option C Explanation: Increase of B with I is not linear. Hence R is false.
44.
Assertion (A): From the slope of the line in Figure, we can find permanent dipole moment of the molecules. Reason (R): Total polarization of a polyatomic gas is given by P = N e + i + μ2p / 3kT)E.
A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option A Explanation: The slope of the line in figure is . Since the total polarization is as given by the expression, we can find the permanent dipole moment of the molecules from the slope.
45.
Assertion (A): If E is available energy state eV and EF is Fermi level, then probability of energy state E being occupied = 0.5.
Reason (R): . A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not correct explanation of A C. A is true but R is false D. A is false but R is true Answer: Option B Explanation: E = EF, f(E) = 0.5.
46.
If a piece of wood is placed in a magnetic field A. the magnetic field will not be affected B. the magnetic lines of force will bend towards the piece C. the magnetic lines of force will bend away from the piece D. the flux may increase or decrease Answer: Option A Explanation: Wood is non-magnetic.
47.
The apparent capacitance at a high angular frequency ω of an air cored capacitor having capacitance C and inductance L is given by A.
B. C. D. Answer: Option B Explanation: The combination can be represented as L and C in series. . Therefore,
.
48.
The number of valence electrons in donor impurity are A. 5 B. 4 C. 3 D. 1 Answer: Option A Explanation: Donor impurity has 5 valence electrons (while silicon has 4 valence electrons). Hence donor impurity can donate electrons.
49.
In a true valence crystal, the bonding between the atoms is accomplished by the sharing of valence electrons. A. True B. False Answer: Option A Explanation: Sharing of valence electrons is a characteristic of true valence crystal.
50.
Which of the following are donor impurities? 1. Gold 2. Phosphorus 3. Boron 4. Antimony 5. Arsenic 6. Indium Select the correct answer using the following codes A. 1, 2, 3 B. 1, 2, 4, 6 C. 3, 4, 5, 6 D. 2, 4, 5 Answer: Option D Explanation: Donor impurities have five valence electrons.
