ELECTRONICS AND COMMUNICATIONS ENGINEERING Materials and Components - Section 2 1.
In crystalline solids, atoms are stacked in a regular manner. True False A. B. Answer: Option A
2.
The temperature below which certain materials are antiferromagnetic and above which they are paramagnetic is called Weiss temperature temperature A. Curie temperature B. Neel temperature C. None of the above D. Answer: Option C
3.
In metals, the average drift velocity of electron per unit field is called mobility. True False A. B. Answer: Option A
4.
Ferrites have a low copper loss A. low eddy current loss B. low resistivity C. higher specific gravity compared to iron D. Answer: Option B Explanation: Resistivity of ferrites is very high as compared to that of iron. Hence eddy currents are much less.
5.
In intrinsic semiconductors, the number of free electrons is equal to the number of mobile holes. True False A. B. Answer: Option A
6.
When a material becomes a superconductor, its resistivity becomes very small A. zero B. about 10% of normal value C. about 20% of normal value D. Answer: Option B superconductor tor has zero zero resistance. resistance. Explanation: A superconduc
7.
In a piezoelectric crystal, the application of mechanical force will cause plastic deformation of crystal A. magnetic dipoles in the crystal B. electrical polarization in the crystal C. shift in Fermi level D. Answer: Option B Explanation: Piezoelectric materials permit conversion of mechanical force into electrical energy.
8.
Consider the following statement If an electric field is applied to an n type semiconductor bar, the electrons and holes move in opposite directions due to their opposite charges. The net currents is 1. both due to electrons and holes with electrons as majority carriers 2. sum of hole and electron currents 3. difference between electron and hole currents. Which of above statements are correct? 1 only A. 1 and 2 B. 2 only C. 3 only D. Answer: Option B Explanation: The net current is sum of currents due to holes and electrons. In n type materials, electrons are majority carriers.
9.
As the temperature of a pure silicon specimen is increased the number of free electrons increases A. the number of holes decreases B. the number of holes increases C. the number of free electrons and holes increases D. Answer: Option D
10.
Assertion (A): In many materials, dielectric polarization causes mechanical distortion. Reason (R): If dielectric polarization causes mechanical distortion then mechanical distortion must cause dielectric polarization. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option C
11.
Semi conducting materials are all elements A. compounds B. elements or compounds C. elements or mixtures D. Answer: Option C Explanation: Many compounds also show semiconducting properties.
12.
Silicon and germanium atoms combine orderly into array of atoms located in repetitive geometric pattern. This pattern is called crystal A. covalent bond B. molecule C. valence bond D. Answer: Option A
13.
In a pure sample of silicon the number of holes and free electrons is always equal A. the number of free electrons is more than the number of holes B. the number of free electrons and holes is equal at low temperature C. the number of free electrons is less than number of holes D. Answer: Option A
14.
Orbital magnetic dipole moment is due to the motion of electron in its orbit around nucleus. True False A. B. Answer: Option A
15.
Assertion (A): ∈r can be determined experimentally by measuring the capacitance of a parallel plate capacitor with and without the dielectric.
. Reason (R): Capacitance of a parallel plate capacitor = Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A
16.
In a homogeneous magnetic field H of a solenoid, the core carries a magnetic dipole moment M per unit volume equal to A. μ0 H B. μr H C. (μr - 1) H D. μoμr H Answer: Option C
17.
The field pattern of a solenoid is similar to that of bar magnet. True False A. B. Answer: Option A
18.
Assertion (A): In a parallel plate capacitor having area of plate 1 m 2 and plate separation 1 m, the capacitance C and resistance R are given by C = ∈0∈' r and R
= where ω is frequency, ∈r ' and ∈r " are real and imaginary parts of dielectric constant. Reason (R): The imaginary part of electric constant is responsible for dielectric losses. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A
19.
Assertion (A): Silicon is the most favoured semiconductor material. Reason (R): PIV for silicon diode is more than that for germanium diode. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option C Explanation: Higher PIV for silicon is a definite advantage.
20.
Assertion (A): When cathode temperature is increased from 2500 K to 2550 K, thermionic emission current may increase by about 50%. Reason (R): Thermionic emission current ∝ T2 e-Ew/k T. Both A and R are true and R is correct explanation of A A.
Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A
21.
In molecules of ionic crystals, orientation polarization is zero. True False A. B. Answer: Option A
22.
Assertion (A): CO2 has no resultant dipole moment but CO has a dipole moment. Reason (R): The structure of CO 2 is O = C = O. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A
23.
For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in a change in o.c voltage A. a change in s.c current B. decrease in resistance C. increase in resistance D. Answer: Option C Explanation: It is the characteristic of a photoconductor that its resistance decreases with increase in illumination.
24.
A permeable substance is one which is strong magnet A. which is a weak magnet B. which is a good conductor C. through which magnetic lines of force can pass easily D. Answer: Option D
25.
When subjected to alternating stresses, an insulating material is characterised by complex dielectric constant ∈' r - j ∈" r . In such materials, the dielectric losses under alternating stress is proportional " ∈ r A. both ∈' r and ∈" r B. ' ∈ r C. (∈" r )2 D. Answer: Option A Explanation: The imaginary part of ∈r gives rise to absorption of energy.
26.
The classes of solid dielectrics are A, B, C, D, E, F, H A. A E B F H C D B. YAEBFHC C. A E B F H C D. Answer: Option C
27.
A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be 2.5 mH A. 5 mH B. 20 mH C. 40 mH D. Answer: Option D Explanation: Inductance is proportional to square of number of turns.
28.
A material which is lightly repelled by a magnetic field is known as diamagnetic material A. non-magnetic material B. ferromagnetic material C. paramagnetic material D. Answer: Option A
29.
Which of the following is the poorest conductor of electricity? Aluminium A. Nichrome B. Copper C. All of the above D. Answer: Option B
30.
The magnetic moment in units of Bohr magneton of a ferrous ion in any ferrite is zero 2 A. B. 4 6 C. D. Answer: Option C
31.
The relationship of hysteresis loss to maximum flux density was first determined by C. Steinmetz A. G.R. Kirchoff B. Mr. Laplace C. Mr. Ampere D. Answer: Option A
32.
In metals the thermal conductivity K and electrical conductivity σ are related as (K/σT) = L, L is known as Lattice constant A. Lorentz number B. Lanevin function C. Larmor number D. Answer: Option B
33.
Assertion (A): If W F is Fermi energy, v is velocity of electron and m is mass of electron,
then . Reason (R): Conductivity of a metal depends on temperature and impurity concentration. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option B
34.
Dielectric constant of transformer oil is about 1 A. B. 10 C. D. Answer: Option B
4 20
35.
Assertion (A): When an electron is revolving in its orbit and magnetic field is also present, the angular frequency of electron will be affected by the magnetic field. Reason (R): In the case of electron revolving in its orbit in the presence of magnetic field, the orbital magnetic dipole moment is not affected by the presence of magnetic field. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option C
36.
In carbon resistor colour code, the third band is red. It indicates two zeros A. three zeros B. multiplier is 0.01 C. multiplier is 0.1 D. Answer: Option A
37.
Rochelle salt is a ferroelectric material. True A. Answer: Option A
B.
False
38.
Paramagnetic materials have permanent magnetic dipoles but interaction between neighboring dipoles is negligible. True B. False A. Answer: Option A
39.
Assertion (A): If difference between static and optical dielectric constant is high, the mechanical compressibility of that material is also high. Reason (R): For soft ions, ionic polarization per unit field is higher than that of hard ions. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A
40.
Assertion (A): In Figure, the intercept of the line on y -axis is equal to N (ae + ai ), where N is number of atoms/m 3, ae is electronic polarizability and a i is ionic polarizability.
Reason (R): ae and ai are independent of temperature.
Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A Explanation: The intercept on y -axis equals N (a e + ai ). This intercept is constant because a e and ai are independent of temperature.
41.
Assertion (A): The optical dielectric constant (i.e., ε r at optical frequencies)of ionic dielectrics is less than static dielectric constant. Reason (R): At optical frequencies, P i = 0. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option A
42.
A piece of iron is placed in a magnetic field the magnetic field will not be affected A. the magnetic lines of force will bend to pass through the piece B. the magnetic lines of force will bend away from the piece C. any of the above depending on type of iron D. Answer: Option B
43.
Assertion (A): Magnetism can be explained by the theory of magnetic domains. Reason (R): The existence of magnetic domains is evident from the Bitter powder patterns. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option B
44.
Ferromagnetic materials shows spontaneous magnetization below a certain temperature A. have resistivity very high as compared to that of iron B. can be used even at microwave frequencies C. all of the above D. Answer: Option D
45.
In a specimen of ferromagnetic material, as the flux density is increased from zero to 2.5 T, µr will increase A. decrease B.
first decrease then increase C. first increase then decrease D. Answer: Option D
46.
Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic. Reason (R): Mean free path of an electron λ, velocity of electron v and mean time between collisions t c are related as λ = v Tc . Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option B
47.
Assertion (A): Copper is a monoatomic solid. Reason (R): In a metal the valence electrons belong to all atoms. Both A and R are true and R is correct explanation of A A. Both A and R are true but R is not correct explanation of A B. A is true but R is false C. A is false but R is true D. Answer: Option B
48.
The heat developed per m 3 per second (W) in a conductor having a conductivity σ and a field E is A. W = σE2 B. W = σE
W= C. D. W = (σE) 0.5 Answer: Option A
49.
The number of valence electrons in acceptor impurity are 5 4 A. B. 3 1 C. D. Answer: Option C
50.
If q is charge on an electron, R is radius of electron orbit and ω is angular velocity of electron rotation, the magnetic dipole moment of electron in orbit is 0.5 qωR A. 0.5 q2ω2R2 B. 0.5 qωR2 C. 0.5 qω2R D. Answer: Option C
