DC Motors Multiple Choice Questions and Answers for Practice

16. 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

17. 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%

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

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

19. 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

20. 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

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

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

22. 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

23. 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

24. Torque developed by a D.C. motor depends upon

1. magnetic field
2. active length of the conductor
3. current flow through the conductors
4. all above factors

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

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

26. Ward-Leonard control is basically a

1. voltage control method
2. field divertor method
3. field control method
4. armature resistance control method

27. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?

1. The motor will stop
2. The motor will continue to run
3. The armature may burn
4. The motor will run noisy

28. When the armature of a D.C. motor rotates, e.m.f. induced is

1. self-induced e.m.f.
2. mutually induced e.m.f.
3. back e.m.f.
4. none of the above

29. When two D.C. series motors are connected in parallel, the resultant speed is

1. more than the normal speed
2. loss than the normal speed
3. normal speed
4. zero

30. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversingand speed control

1. drum type controller is used
2. three point starter is used
3. four point starter is used
4. all above can be used