Materials and Components – Section 2(Page 5)

Materials and Components – Section 2

41. Assertion (A): The optical dielectric constant (i.e., εr at optical frequencies)of ionic dielectrics is less than static dielectric constant.

Reason (R): At optical frequencies, Pi = 0.

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

42. A piece of iron is placed in a magnetic field
A. the magnetic field will not be affected
B. the magnetic lines of force will bend to pass through the piece
C. the magnetic lines of force will bend away from the piece
D. any of the above depending on type of iron

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.

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

44. Ferromagnetic materials
A. shows spontaneous magnetisation below a certain temperature
B. have resistivity very high as compared to that of iron
C. can be used even at microwave frequencies
D. all of the above

Answer: Option D

45. In a specimen of ferromagnetic material, as the flux density is increased from zero to 2.5 T, µr will
A. increase
B. decrease
C. first decrease then increase
D. first increase then decrease

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 tc are related as λ = vTc.

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

47. Assertion (A): Copper is a monoatomic solid.

Reason (R): In a metal the valence electrons belong to all atoms.

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

48. The heat developed per m3 per second (W) in a conductor having a conductivity σ and a field E is
A. W = σE2
B. W = σE
C. W =
D. W = (σE)0.5

Answer: Option A

49. The number of valence electrons in acceptor impurity are
A. 5
B. 4
C. 3
D. 1

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
A. 0.5 qωR
B. 0.5 q2ω2R2
C. 0.5 qωR2
D. 0.5 qω2R

Answer: Option C

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