Materials and Components – Section 3(Page 4)

Materials and Components – Section 3

31. Thermistor is used in
A.temperature measurement
B.temperature control
C.high temperature alarm circuits of devices
D.all of the above

Answer: Option D

32. Nichrome is used for
A.overhead line wires
B.heater coils
C.lamp filaments
D.all of the above

Answer: Option B

33. The electric dipole moment of a neutral system of point charges Q1, Q2…. is
Qiri . The charges Qi
A.must be all positive
B.must be all negative
C.must be such that Qi = 0
D.either (a) or (b)

Answer: Option C

Explanation:

The system is neutral and hence sum is zero.

34. The class of insulation of impregnated paper is
A.A
B.B
C.C
D.F

Answer: Option A

35.Assertion (A): The resistance of a copper specimen changes by about 22% when temperature is increased from room temperature to 700°C.

Reason (R): The physical properties of a material are determined mostly by the extent of impurities.

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

Explanation:

The increase of resistance with temperature is governed by temperature coefficient of resistance.

36. Assertion (A): For most metals, Fermi energy EF is less than 10 eV.

Reason (R): Fermi level of a metal is given by EF = 3.64 x 10-19 (n)2/3 where n is number of free electrons/m3 of metal.

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

37. The capacitance of an insulated conducting sphere of radius R in vacuum is
A.2p0R
B.4p0R
C.4p0R2
D.4p

Answer: Option B

38. The transition of electron from energy level W1 to W2 is associated with emission or absorption of electro magnetic radiation of frequency f such that
A.hf = |W1 – W2|
B.|W1 – W2|f = h
C.hf = 0.5|W1 – W2|
D.(hf)2 = |W1 – W2|

Answer: Option A

39. A material has N spins per m3. If Np are the dipoles per m3 parallel to field and Na are the dipoles per m3 anti-parallel to field, the magnetisation is
A.
B.
C.
D.

Answer: Option A

40. Even at room temperature, an intrinsic semiconductor has some holes. These holes are due to
A.electron
B.doping
C.thermal energy
D.free electrons

Answer: Option C

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