Electrical Engineering Materials MCQ

61. Which of the following properties is not correct for a superconductor in its superconducting stage?

(a) Its resistivity is zero.
(b) Magnetic flux density inside the conductor is zero.
(c) Its relative permeability is unity.
(d) Its magnetic susceptibility is negative.

62. Superconducting metal in superconducting state has relative permeability of

(a) more than one.
(c) zero.
(b) one.
(d) negative.

63. What is the magnetic susceptibility of an ideal superconductor?

(a) 1
(b) -1
(c) 0
(d) Infinite.

64. The transition temperature of mercury at which it becomes superconductive is

(a) 4.12°F
(b) 4.12°C
(c) 4.12 K
(d) 41.2 K

65. Consider the following properties:

1. Perfect diamagnetism.
2. Ionic conductivity.
3. Magnetic field causes an increase in transition temperature.
4. Loss of superconductivity in long circular wire by large currents.

Which of these properties are exhibited by a superconductor?
(a) 1, 2 and 3.
(b) 2, 3 and 4.
(c) 1, 3 and 4.
(d) 1, 2 and 4.

66. Which of the following statements is NOT true?

(a) Superconductor show perfect diamagnestism.
(b) Superconductors have almost zero resistivity.
(c) The external magnetic field has no effect on superconductors.
(d) Entropy increases on going from superconducting state to normal state.

67. Consider the following statements about superconductors:

1. The temperature at which the conductor becomes a superconductor is called transition temperature.
2. Superconductors repel magnetic flux lines.
3. All superconductors are paramagnetic materials.
4. Superconductors become normal when placed in a magnetic field of certain critical value.

Which of the above statements are correct?
(a) 1 and 2 only.
(b) 2 and 4 only.
(c) 1, 2 and 4 only.
(d) 1, 2, 3 and 4.

68. Materials in superconducting state have the property of

(a) absorbing magnetic field.
(b) repelling magnetic field.
(c) absorbing electric field.
(d) repelling electric field.

69. As temperature falls below the transition temperature, the value of critical magnetic field of a superconductor

(a) remains unchanged.
(b) increases.
(c) decreases.
(d) first increases, reaches a peak and then decreases.

70. The energy gap of a superconductor

(a) is independent of temperature.
(b) increases with temperature.
(c) is maximum at a critical temperature.
(d) is minimum at a critical temperature.

71. On which of the following factors does the value of critical current density in a superconductor depend?

(a) Temperature.
(b) Applied magnetic field.
(c) Temperature and applied magnetic field.
(d) Silsbee’s rule.

72. Materials, whose specific resistance abruptly falls at very low temperature are called

(a) conductors.
(b) superconductors.
(c) semiconductors.
(d) insulators.

73. Superconductivity is due to

(a) all electrons having fermi energy at 0 K.
(b) all electrons interacting in the superconducting state.
(c) crystal structure having no atomic vibration at 0 K.
(d) crystal structure having infinite atomic vibrations at 0 K.

74. The structure sensitive property of a superconductor is

(a) transition temperature.
(b) critical magnetic field.
(c) critical current density.
(d) none of the above.

75. Consider the following statements: Superconductivity in a material can be destroyed by

1. increasing the temperature above a certain limit.
2. applying a magnetic field above a certain limit.
3. passing a current, above a certain limit, through the material.
4. decreasing the temperature to a point below the critical temperature.

Of these statements
(a) 2, 3 and 4 are correct.
(b) 1, 3 and 4 are correct.
(c) 1, 2 and 3 are correct.
(d) 1, 2 and 4 are correct.

76. Superconductivity is destroyed

(a) At high temperature.
(b) At high magnetic field.
(c) In presence of magnetic impurities.
(d) In all the above cases.

77. The magnetic susceptibility of an ideal type I superconductor in the superconductivity state is

(a) α
(b) -1
(c) between 0 and 1
(d) zero.

78. What type of magnetic behavior is observed in a type I superconductor ?

(a) Perfect diamagnetism.
(b) Perfect paramagnetism.
(c) Perfect ferromagnetism.
(d) Perfect ferrimagnetism.

79. Superconductivity is observed for

(a) dc and low frequency.
(b) ac and high frequency.
(c) infrared frequencies.
(d) frequencies having no effect.

80. In a superconductor the value of critical density depends upon

(a) temperature.
(b) magnetic field strength.
(c) both (a) and (b).
(d) none of these.