D.C. Machines

81. The size of the feeder is determined primarily by

1. the current it is required to carry.
2. the percent variation of voltage in the feeder.
3. the voltage across the feeder.
4. the distance of transmission.

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82. The sole purpose of a commutator in a dc generator is to

1. increase output voltage
2. reduce sparking at brushes
3. provide smoother output
4. convert the induced ac into dc

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83. The speed of a dc motor can be controlled by varying

1. its flux per pole
2. resistance of armature circuit
3. applied voltage
4. all of the above

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84. If a transformer primary is energized from a square wave voltage source, its output voltage will be

1. A square wave.
2. A sine wave.
3. A triangular wave.
4. A pulse wave.

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85. The speed-torque characteristics of a DC series motor are approximately similar to those of the _________ motor.

1. universal
2. synchronous
3. DC shunt
4. two-phase

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86. The starting torque of a 1-phase induction motor is

1. High
2. Medium
3. Low
4. Zero

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87. The stator core of the induction motor is made of

1. Laminated cast iron
2. Mild steel
3. Silicon steel stampings
4. Soft wood

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88. The synchronous speed of a linear induction motor does not depend on

1. Width of pole pitch
2. Number of poles
3. Supply frequency
4. Any of the above

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89. The Ta/Ia graph of a dc series motor is a

1. Parabola from no load to overload
2. Straight line throughout
3. Parabola throughout
4. Parabola upto full load and a straight line at overloads

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90. The thrust developed by a linear induction motor depends on

1. Synchronous speed
2. Rotor input
3. Number of poles
4. both A and B

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