Materials and Components – Section 5(Page 3)

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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