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Materials and Components – Section 4(Page 2)

1 Comment / Electronics and Communications

Materials and Components – Section 4

11. The equation D = ∈0∈r E refers only to isotropic materials.
A. True
B. False

Answer: Option A
12. When a ferromagnetic substance is magnetised there are small changes in dimensions. This phenomenon is called
A. hysteresis
B. magnetostriction
C. diamagnetism
D. dipolar relaxation

Answer: Option B
13. Assertion (A): In some materials, ∈r is independent of temperature while in others, ∈r depends on temperature.

Reason (R): If permanent dipoles are absent, ∈r varies with 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
14. An electron in a homogeneous magnetic field and having velocity perpendicular to the direction of field moves
A. perpendicular to the field
B. along the field
C. along a straight line inclined at 45° to field
D. in a circular path

Answer: Option D
15. Spontaneous polarization occurs in ferroelectric materials.
A. True
B. False

Answer: Option A
16. For a given value (n) of principle quantum number, the number of possible electronic states are
A. n
B. n2
C. n3
D. n

Answer: Option B

Explanation:

The total number of states corresponding to a given value of n is equal to

(2l + 1) = 1 + 3 + …. + [2(n-1) + 1] = n2.
17. Electrical conductivity of metals expressed in ohm-1 m-1 is of the order of
A. 1010
B. 105
C. 10-4
D. 10-6

Answer: Option B

Explanation:

Conductivity is reciprocal of resistivity. Since resistivity of metals is around 10-7 ohm-m, conductivity is about 107 ohm-1 m-1. So 105 is the nearest value.
18. In a metal the probability of a state 0.1 eV below Fermi level being occupied
A. is more than the probability of state 0.1 eV above Fermi level being occupied
B. is the same as the probability of state 0.1 eV above Fermi level being occupied
C. is less than the probability of state 0.1 eV above Fermi level being occupied
D. may be equal to or more or less than the probability of state 0.1 eV above Fermi level being occupied

Answer: Option A
19. An homogeneous dielectric material is subjected to an electric field E. If a small cavity is made inside the material, the electric field intensity inside and outside the cavity are different.
A. True
B. False

Answer: Option B

Explanation:

The electric field intensity inside and outside the cavity are equal.
20. A dielectric is subjected to alternating field. The dielectric losses are potential to
A. real part of dielectric constant
B. imaginary part of dielectric constant
C. both real and imaginary parts of dielectric constant
D. either real or imaginary part of dielectric constant

Answer: Option B

Explanation:

Absorption of energy is proportional to imaginary part of complex dielectric constant.

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