81. The value of critical field below the transition temperature will
(c) not be affected at all.
(d) none of these.
82. At transition temperature the value of critical field is
84. According to the BCS theory, a material goes into superconducting state when electron-pairs participate in the following events:
- Lattice distorts as a free electron A attracts a lattice ion.
- Temperature is decreased.
- Energy of electron B is lowered and it forms a pair with electron A.
- A photon is created which interacts with electron B.
The correct sequence of occurrence of these events is :
(a) 2, 1, 3, 4.
(b) 1, 2, 3, 4.
(c) 2, 1, 4, 3.
(d) 1. 2, 4, 3.
85. The magnetic field at which a superconductor remains in its superconducting state at a temperature less than the transition temperature is
(b) Greater than the critical field corresponding to the given temperature.
(c) Less than the critical field corresponding to the given temperature.
(d) Equal to the critical field corresponding to the transition temperature.
86. The transition temperature of superconducting material is changed by which one of the following ?
(a) Electric field.
(b) Magnetic field.
(c) Mechanical stress.
(d) None of the above.
87. Consider the following statements in connection with superconductors:
- Transition temperature of a superconductor can be reduced by the application of a magnetic field.
- Transition from the superconducting to normal state under the influence of a magnetic field is irreversible.
Which of the statements given above is/are correct?
(a) 1 only.
(b) 2 only.
(c) Both 1 and 2.
(d) Neither 1 nor 2.
88. Which one of the following statements is correct? Superconductors are popularly used for
(a) generating very strong magnetic field.
(b) reducing I2R losses.
(c) generating electrostatic field.
(d) generating regions free from magnetic field.
89. A superconductor may be used for generating
(d) magnetic field.
90. Annealing of metals
(a) removes internal stresses.
(b) increases conductivity.
(c) increases the grain size.
(d) both (a) and (b).
91. Cold working operation
(a) increases conductivity.
(b) increases resistivity.
(c) converts a thicker wire into a thin wire.
(d) removes internal stresses.
92. The property of materials by which they can be drawn into wires is known as
93. The property of material by which it can be rolled into sheets is called the
94. The formation of oxide film on a metal due to atmospheric exposure reduces
(a) creep limit.
(d) none of these.
95. Gold, silver and copper are good electrical conductors because their outer orbits contain
(a) one electron.
(b) two electrons.
(c) one proton.
(d) more than two electrons.
96. The best variety of copper from the point of view of electrical conductivity is
(a) pure annealed copper.
(b) hard drawn copper.
(c) induction hardened copper.
(d) copper containing silicon traces.
97. Which one of the following is the poorest electrical conductor ?
98. Copper, though costly, finds use in windings for electrical machines because
(a) it offers low contact resistance.
(b) it can be easily soldered and welded.
(c) it gives less bulky windings leading to compact machines.
(d) all of the above.
99. Copper and aluminum are not used for heating elements. This is due to
(a) their low melting points.
(b) their great tendency for oxidation.
(c) low resistivity leading to requirement of very large length of wires.
(d) all of the above.
100. Which one of the following metals has the lowest temperature coefficient of resistance ?
101. Conductivity of aluminum is……….time of that of copper.
102. Copper has low…….. in comparison to that of aluminum.
(a) melting point
(b) specific gravity
103. In many applications copper is being replaced by aluminum. This is due to
(a) low cost, abundantly availability and low specific gravity of aluminum in comparison to that of copper.
(b) low resistivity of aluminum in comparison to that of copper.
(c) more ductility and malleability of aluminum in comparison to that of copper.
(d) low temperature coefficient of resistance of aluminum in comparison to that of copper.
Electrical Engineering Materials MCQ
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