Electrical Engineering Materials (GATE + AE + PSU level)

 51. The electrical resistivity of insulators is generally of the order of

A) $10^{-6}$ Ω-m
B) $10^{6}$ Ω-m
C) $10^{10}$ Ω-m
D) $10^{16}$ Ω-m
Ans: D

52. Magnetic materials in which magnetization is proportional to the magnetizing field are called
A) Diamagnetic
B) Paramagnetic
C) Ferromagnetic
D) None of these
Ans: B

53. The main function of a dielectric in a capacitor is to
A) Increase the breakdown voltage
B) Reduce energy loss
C) Store energy in the electric field
D) All of these
Ans: D

54. The resistivity of a pure semiconductor
A) Increases with temperature
B) Decreases with temperature
C) Is constant
D) Becomes infinite
Ans: B

55. The most common material used for making resistors is
A) Nichrome
B) Copper
C) Aluminum
D) Steel
Ans: A

56. The permeability of non-magnetic materials is approximately equal to
A) 1
B) 4π × 10⁻⁷
C) Zero
D) Infinity
Ans: A

57. The material used for making core of transformers should have
A) High permeability and low hysteresis loss
B) Low permeability and high hysteresis loss
C) High permeability and high eddy current loss
D) Low permeability and low conductivity
Ans: A

58. In a dielectric material, as the temperature increases, dielectric strength generally
A) Increases
B) Decreases
C) Remains constant
D) Becomes infinite
Ans: B

59. The resistivity of a semiconductor lies between
A) Metals and insulators
B) Metals and superconductors
C) Insulators and conductors
D) None
Ans: A

60. The relative permittivity of most insulating materials lies between
A) 1 and 5
B) 5 and 10
C) 10 and 20
D) 20 and 50
Ans: A

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61. The property of material to retain magnetism is called
A) Permeability
B) Retentivity
C) Coercivity
D) Hysteresis
Ans: B

62. When a ferromagnetic material is heated above its Curie point, it becomes
A) Diamagnetic
B) Paramagnetic
C) Non-magnetic
D) Superconducting
Ans: B

63. The atomic structure of good conductors has
A) Tightly bound electrons
B) Free electrons
C) No electrons
D) Only covalent bonds
Ans: B

64. The drift velocity of electrons is proportional to
A) Current density
B) Resistivity
C) Mobility
D) A and C both
Ans: D

65. The substance which offers high resistance to the flow of electric current is
A) Conductor
B) Semiconductor
C) Insulator
D) Superconductor
Ans: C

66. In a paramagnetic material, the magnetic dipoles
A) Align perfectly
B) Align partially with field
C) Do not align
D) Oppose magnetic field
Ans: B

67. The phenomenon of polarization occurs in
A) Conductors
B) Dielectrics
C) Semiconductors
D) Magnetic materials
Ans: B

68. Which of the following is not a ferromagnetic material?
A) Cobalt
B) Nickel
C) Chromium
D) Iron
Ans: C

69. The thermal conductivity of metals is due to
A) Free electrons
B) Lattice vibrations
C) Protons
D) Both A and B
Ans: D

70. The breakdown strength of air is approximately
A) 1 kV/cm
B) 3 kV/mm
C) 30 kV/cm
D) 300 kV/mm
Ans: B

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71. The core of large generators is laminated to reduce
A) Hysteresis loss
B) Eddy current loss
C) Both losses
D) None
Ans: B

72. A material which exhibits magnetization opposite to the applied field is
A) Ferromagnetic
B) Paramagnetic
C) Diamagnetic
D) Ferrimagnetic
Ans: C

73. Superconductors have
A) Infinite resistance
B) Zero resistance
C) Very high resistance
D) Constant resistance
Ans: B

74. Copper losses are reduced by
A) Using smaller conductors
B) Using conductors of higher resistivity
C) Using larger cross-section conductors
D) Increasing frequency
Ans: C

75. The resistivity of aluminum compared to copper is
A) Lower
B) Same
C) Higher
D) Zero
Ans: C

76. Which of the following is a ferrimagnetic material?
A) Ferrite
B) Nickel
C) Iron
D) Cobalt
Ans: A

77. The energy loss per cycle per unit volume of magnetic material is given by
A) Area of hysteresis loop
B) Flux density
C) Permeability
D) None
Ans: A

78. Which of the following is used for shielding high-frequency fields?
A) Steel
B) Copper
C) Aluminum foil
D) Lead
Ans: C

79. The current density is directly proportional to
A) Electric field
B) Resistivity
C) Mobility
D) A and C both
Ans: D

80. The conductivity of intrinsic semiconductors increases with
A) Decrease in temperature
B) Increase in temperature
C) Remains constant
D) None
Ans: B

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81. The polarization in dielectrics under static field is called
A) Ionic polarization
B) Orientation polarization
C) Electronic polarization
D) Total polarization
Ans: C

82. Which of the following materials is used as dielectric in capacitors?
A) Glass
B) Air
C) Mica
D) All of these
Ans: D

83. The magnetization curve of a ferromagnetic material is called
A) Hysteresis loop
B) Load curve
C) B–H curve
D) Flux curve
Ans: A

84. The relative permeability of paramagnetic materials is
A) Less than 1
B) Equal to 1
C) Slightly more than 1
D) Very high
Ans: C

85. For superconductivity, the material must be cooled below its
A) Melting point
B) Critical temperature
C) Curie temperature
D) Boiling point
Ans: B

86. The material with least eddy current loss is
A) Laminated steel
B) Solid iron
C) Cast steel
D) Mild steel
Ans: A

87. The dielectric loss occurs due to
A) Polarization
B) Ionization
C) Hysteresis in dielectric
D) Leakage current
Ans: C

88. Conductors obey
A) Ohm’s Law
B) Faraday’s Law
C) Ampere’s Law
D) Gauss’s Law
Ans: A

89. For good conducting materials, temperature coefficient of resistance is
A) Negative
B) Zero
C) Positive
D) Infinite
Ans: C

90. Silicon steel is preferred in transformer cores because
A) It reduces eddy current losses
B) It increases weight
C) It decreases flux density
D) It increases resistance
Ans: A

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91. The main function of a core in an electrical machine is to
A) Support windings
B) Conduct magnetic flux
C) Reduce mechanical losses
D) None
Ans: B

92. The resistivity of metals mainly depends on
A) Crystal structure
B) Temperature
C) Magnetic field
D) Mechanical stress
Ans: B

93. The process of making steel more magnetic is
A) Hardening
B) Annealing
C) Tempering
D) None
Ans: B

94. Insulating varnishes are used in electrical machines for
A) Reducing resistance
B) Preventing moisture absorption
C) Increasing losses
D) Increasing conductivity
Ans: B

95. The main disadvantage of ferrite materials is
A) High resistivity
B) Brittle nature
C) Low permeability
D) High density
Ans: B

96. In thermistors, resistance changes with
A) Voltage
B) Frequency
C) Temperature
D) Current
Ans: C

97. Pure silicon behaves as
A) Conductor
B) Insulator
C) Semiconductor
D) Superconductor
Ans: C

98. Dielectric materials are used in
A) Transformers
B) Capacitors
C) Inductors
D) Resistors
Ans: B

99. The main requirement of a material used for electric heating is
A) Low resistivity
B) High resistivity and high melting point
C) Low melting point
D) Magnetic property
Ans: B

100. The best magnetic material for low-frequency applications is
A) Silicon steel
B) Ferrite
C) Cast iron
D) Cobalt
Ans: A