Electrical Engineering Materials

51. Steel wire is used as

1. overhead telephone wire
2. earth wire
3. core wire of ACSR
4. all of the above

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52. Substances whose specific resistance abruptly decreases at very low temperature are called

1. insulators
2. conductors
3. semiconductors
4. superconductors

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53. Super conductivity can be destroyed by

1. adding impurities
2. reducing temperatures
3. application of magnetic field
4. any of the above

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54. Superconducting metal in super conducting state has relative permeability of

1. zero
2. one
3. negative
4. more than one

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55. Superconductivity is observed for

1. infrared frequencies
2. d.c. and low frequency
3. a.c. and high frequency
4. frequencies having no effect

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56. Superconductors are becoming popular for use in

1. generating very strong magnetic field
2. manufacture of bubble memories
3. generating electrostatic field
4. generating regions free from magnetic field

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57. Surface resistance of an insulating material is reduced due to the

1. smoky and dirty atmosphere
2. humidity in the atmosphere
3. both (a) and (b)
4. neither (a) nor (b)

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58. The carbon percentage is least in

1. low carbon steel
2. wrought iron
3. cast iron
4. malleable iron

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59. The coils of D.C. motor starter are wound with wire of

1. copper
2. kanthal
3. manganin
4. nichrome

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60. The conduction of electricity, in semiconductors, takes place due to movement of

1. positive ions only
2. negative ions only
3. positive and negative ions
4. electrons and holes

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