D.C. Motors

81. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by

1. reducing the field current
2. decreasing the armature current
3. increasing the armature current
4. increasing the excitation current

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82. The speed of a D.C. shunt motor more than its full-load speed can be obtained by

1. decreasing the field current
2. increasing the field current
3. decreasing the armature current
4. increasing the armature current

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83. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is

1. 2.36%
2. 4.76%
3. 6.77%
4. 8.84%

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84. The starting resistance of a D.C. motor is generally

1. low
2. around 500 Q
3. 1000 Q
4. infinitely large

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85. The total losses in a well designed D.C. generator of 10 kW will be nearly

1. 100 W
2. 500 W
3. 1000 W
4. 1500 W

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86. The type of D.C. motor used for shears and punches is

1. shunt motor
2. series motor
3. differential compoutid D.C. motor
4. cumulative compound D.C. motor

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87. These days D.C. motors are widely used in

1. pumping sets
2. air compressors
3. electric traction
4. machine shops

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88. Three point starter can be used for

1. series motor only
2. shunt motor only
3. compound motor only
4. both shunt and compound motor

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89. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.

1. Ward Leonard control
2. rheostatic control
3. any of the above method
4. none of the above method

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90. Usually wide and sensitive speed control is desired in case of

1. centrifugal pumps
2. elevators
3. steel rolling mills
4. colliery winders

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