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Materials and Components – Section 3(Page 4)

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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. 2p∈0R
B. 4p∈0R
C. 4p∈0R2
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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