D.C. Motors

41. In a D.C. shunt motor, speed is

1. independent of armature current
2. directly proportional to the armature current
3. proportional to the square of the current
4. inversely proportional to the armature current

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42. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be

1. almost negligible
2. rated full-load current
3. less than full-load current
4. more than full-load current

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43. In a differentially compounded D.C. motor, if shunt field suddenly opens

1. the motor will first stop and then run in opposite direction as series motor
2. the motor will work as series motor and run at slow speed in the same direction
3. the motor will work as series motor and run at high speed in the same direction
4. the motor will not work and come to stop

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44. In a manual shunt motor starter

1. over load relay is connected in series and no volt relay in parallel with the load
2. over load relay is connected in parallel and no volt relay in series with the load
3. over load relay and no volt relay are both connected in series with the load
4. over load relay and no volt relay are both connected in parallel with the load

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45. In case of conductively compensated D.C. series motors, the compensating winding is provided

1. as separately wound unit
2. in parallel with armature winding
3. in series with armature winding
4. in parallel with field winding

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46. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because

1. back e.m.f. is equal to armature drop
2. armature drop is negligible
3. flux is proportional to armature current
4. flux is practically constant in D:C. shunt motors

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47. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will

1. remain unchanged
2. reduce to one-fourth value
3. increase four folds
4. be doubled

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48. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be

1. 100%
2. around 90%
3. anywhere between 75% and 90%
4. less than 50%

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49. In D.C. machines fractional pitch winding is used

1. to improve cooling
2. to reduce copper losses
3. to increase the generated e.m.f.
4. to reduce the sparking

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50. In D.C. machines the residual magnetism is of the order of

1. 2 to 3 per cent
2. 10 to 15 per cent
3. 20 to 25 per cent
4. 50 to 75 per cent

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