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Materials and Components – Section 5(Page 3)

1 Comment / Electronics and Communications

Materials and Components – Section 5

21.  The dipole moment per unit volume P as a function of E for an insulator is
A. P = ∈0 E(∈r)
B. P = ∈0 E
C. P = ∈0(∈r – 1) E
D. P =

Answer: Option C
22.  A good dielectric should have
A. low losses
B. good heat conductivity
C. high intrinsic strength
D. all of the above

Answer: Option D
23.  Magnetic hysteresis phenomenon is explained by
A. motion of domain walls
B. motion of domain walls and domain rotation
C. domain rotation
D. none of the above

Answer: Option B
24.  If a metal specimen has n valence electrons per m3 each having charge e and mass m and t is the relaxations time, the conductivity is
A.
B.
C.
D.

Answer: Option B
25.  The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m2) and dT/dx (°C per metre) is
A. Q = K(dT/dx)
B. Q = – K(dT/dx)
C. K = Q(dT/dx)
D. dT/dx = – QK

Answer: Option B
26.  As per Matthiessen’s rule, the total resistivity r of a conductor can be written as r = ri + aT, where ri and a are constants and T is absolute temperature. At very low temperatures
A. aT = 0
B. aT > ri
C. aT ∼ ri
D. aT < ri

Answer: Option D

Explanation:

At very low temperatures a T → 0. Since resistivity has a finite value even at low temperature, a T < ri.
27.  Consider the following statement: In case of a superconductor

  1. B = 0
  2. μr is high
  3. diamagnetism is high
  4. transition temperature varies with isotopic mass.

Of the above statements
A. 1 and 2 are correct
B. 2, 3, 4 are correct
C. 1, 3, 4 are correct
D. 2, 4 are correct

Answer: Option C
28. Assertion (A): In liquids and glassy substances, dielectric losses occur.

Reason (R): The orientation polarization in many substances is frequency dependent.
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
29.  A single layer air cored coil has n turns and inductance L. If a new coil is formed by having 2n turns while keeping the coil length and diameter the same, the new inductance is
A. 0.5 L
B. L
C. 2 L
D. 4 L

Answer: Option D

Explanation:

Inductance is proportional to square of number of turns.
30.  The colour code on a carbon resistor is yellow-violet-orange. The value of resistance is
A. 17000 Ω
B. 27000 Ω
C. 37000 Ω
D. 47000 Ω

Answer: Option D

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