Electrical Engineering Materials MCQ

41. The resistivity of metal is a function of temperature because

(a) the magnetic properties change with the variations in temperature.
(b) the amplitude of vibrations of the atoms varies with the temperature.
(c) the electron density varies with the temperature.
(d) none of these.

42. The conductivity of a metal is determined by

(a) the number of valence electrons per atom.
(b) the electron concentration and the mobility of the free electrons.
(c) both (a) and (b).
(d) none of these.

43. The factor(s) which affect(s) the resistivity of the material is/are

(a) mechanical stress.
(b) alloying.
(c) temperature
(d) age hardening
(e) cold working.
(f) all of these.

44. According to Wiedemann-Franz law the ratio of thermal conductivity to electrical conductivity of a conductor is

(a) independent of temperature.
(b) directly proportional to temperature.
(c) inversely proportional to temperature.
(d) inversely proportional to square of temperature.

45. Consider the following statements:

If the temperature is increased, the resistivity of a metal increases because of

1. decrease in carrier concentration.
2. an increase in the extent of scattering of carriers.
3. increase in density of impurity.

Of these statements
(a) 1, 2 and 3 are correct.
(b) 2 alone is correct.
(c) 1 alone is correct.
(d) 2 and 3 are correct.

46. Consider the following statements: Electrical conductivity of a metal has negative temperature coefficient since

1. electron concentration increases with temperature.
2. electron mobility decreases with temperature.
3. electron-lattice scattering increases with temperature.

Which of the statements given above are correct?
(a) 1, 2, and 3.
(b) Only 1 and 2.
(c) Only 2 and 3.
(d) Only 1 and 3.

47. The correct sequence of increasing order of electrical resistivity of the given materials is

(a) diamond, doped germanium, silicon, gold.
(b) gold, silicon, doped germanium, diamond.
(c) gold, doped germanium, silicon, diamond.
(d) gold, diamond, silicon, doped germanium.

48. What is the correct arrangement of the following alloys in decreasing order of resistivity?

(a) German silver – constantan – monel metal.
(b) German silver – monel metal – constantan.
(c) Constantan – monel metal – German silver.
(d) Constantan – German silver- monel metal.

49. In metals, resistivity is composed of two parts one part is characteristic of the particular substance. The other part is due to

(a) applied voltage.
(b) crystal imperfections.
(c) applied magnetic field.
(d) supplied thermal energy.

50. Consider the following properties pertaining to an alloy used as a precision resistor:

1. Uniform resistance.
2. Stable resistance.
3. Zero or low temperature coefficient of resistivity.

Which of these properties are desirable?
(a) 1, 2 and 3.
(b) 1 and 2.
(c) 1 and 3.
(d) 2 and 3.

51. Which one of the following is correct? As frequency increases, the surface resistance of a metal

(a) decreases.
(b) increases.
(c) remains unchanged.
(d) varies in an unpredictable manner.

52. The conductivity of a conducting material on being subject to critical magnetic field changes to

(a) normal state.
(b) unstable state.
(c) temperature-independent state.
(d) temperature-dependent state.

53. Which one of the following statements is correct for four-point probe method of determining resistivity?

(a) The sample must be extrinsic.
(b) The current source is connected to the two inner probes.
(c) One probe point must inject minority carriers.
(d) Current flows only in a small area of the sample.

54. The factor that generally affects the resistivity of electrical conductors is

(a) composition.
(b) size.
(c) temperature.
(d) pressure.

55. The resistivity of a conductor can be reduced by

(a) increasing its temperature.
(b) reducing its temperature.
(c) increasing its vibrations.
(d) reducing its vibrations.

56. With the fall in temperature, the resistivity of all normal metals

(a) remains unaffected.
(b) increases.
(c) tends to be zero.
(d) decreases first and then increases.

57. Among following which conductor has highest conductivity?

(a) Cu
(b) Al
(c) Ag
(d) Mg

58. Consider the following statements with regard to manufacture of a standard resistor:

1. The material should be of high resistivity and low temperature coefficient.
2. Resistors are shielded against magnetic field.
3. Nickel-chromium is best suited for resistance of high value.

Which of the above statements is/are correct?
(a) 1 and 2 only.
(b) 1 only.
(c) 1 and 3 only.
(d) 3 only.

59. The following data are obtained by measurement on gold:

Density = 19.32 gm/cc
Resistivity = 2.42 µΩ/cm
Atomic weight = 197.2

The mobility of elections in gold is
(a) 4.39 x 10^-3 m²/V-sec.
(b) 4.39 x 10^-2 m²/V-sec.
(c) 4.39 m²/V-sec.
(d) 4.39 x 10³ m²/V-sec.

60. A material is said to be superconductor when its resistance is

(a) zero.
(b) very small.
(c) negative.
(d) none of these.