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d c motors MCQs

Practise focused d c motors questions with marked answers for exam preparation and subject revision.

d c motors Mcqs
1. When two D.C. series motors are connected in parallel, the resultant speed is____________?
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A. more than the normal speed

B. normal speed

C. zero

D. loss than the normal speed

2. For starting a D.C. motor a starter is required because___________?
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A. it starts the motor

B. it limits the speed of the motor

C. none of the above

D. it limits the starting current to a safe value
3. Which D.C. motor is preferred for elevators ?
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A. Cumulative compound motor

B. Series motor

C. Differential compound motor

D. Shunt motor

4. The size of poxvirus is_______________?
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A. 250 nm

B. 200 nm

C. 20 nm

D. 300 nm
5. The type of D.C. motor used for shears and punches is_____________?
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A. differential compoutid D.C. motor

B. cumulative compound D.C. motor

C. series motor

D. shunt motor

6. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
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A. Shunt motor

B. Differentially compound motor

C. Series motor

D. Cumulative compound motor

7. Kingdom Protoctista includes_______________?
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A. Prokaryotic organisms

B. Fungi

C. Eu-cariotiquic organisms

D. Unicellular organisms
8. No-load speed of which of the following motor will be highest ?
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A. Differentiate compound motor

B. Shunt motor

C. Series motor

D. Cumulative compound motor

9. Which D.C. motor will be preferred for machine tools ?
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A. Shunt motor

B. Differential compound motor

C. Series motor

D. Cumulative compound motor

10. If a D.C. motor is connected across the A.C. supply it will_______________?
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A. run at lower speed

B. burn due to heat produced in the field winding by .eddy currents

C. not run

D. run at normal speed

11. Which of the following application requires high starting torque ?
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A. Air blower

B. Locomotive

C. Lathe machine

D. Centrifugal pump

12. Differentially compound D.C. motors can find applications requiring___________?
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A. high starting torque

B. frequent on-off cycles

C. low starting torque

D. variable speed

13. To get the speed of D.C, motor below the normal without wastage of electrical energy is used?
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A. Ward Leonard control

B. none of the above method

C. rheostatic control

D. any of the above method

14. According to Flemings left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of_________________?
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A. none of the above

B. current in the conductor aovtaat of conductor

C. resultant force on conductor

15. The direction of rotation of a D.C. series motor can be changed by___________?
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A. either of A. and B. above

B. None of the above

C. interchanging field terminals

D. interchanging supply terminals

16. A D.C. series motor is that which______________?
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A. can be started easily without load

B. has its field winding consisting of thick wire and less turns

C. has almost constant speed

D. has a poor torque

17. If the field of a D.C. shunt motor gets opened while motor is running______________?
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A. the motor will continue to nuvat constant speed

B. the armature current will reduce

C. the speed of motor will be reduced %

D. the motor will attain dangerously high speed 1
18. Starters are used with D.C. motors because______________?
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A. back e.m.f. of these motors is zero initially

B. these motors have high starting torque

C. to restrict armature current as there is no back e.m.f. while starting

D. these motors are not self-starting

19. In D.C. shunt motors as load is reduced__________________?
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A. the speed will remain almost/constant

B. the speed will reduce

C. the speed will increase abruptly

D. the speed will increase in proportion to reduction in load

20. D.C. series motors are used______________?
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A. where load changes frequently

B. where constant operating speed is needed

C. where load is constant

D. in none of the above situations
21. The main disadvantage of the Ward-Leonard control method is______________?
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A. all of the above

B. high maintenance cost

C. low efficiency at Hght loads

D. high initial cost

22. If the field winding resistance of a DC shunt motor is increases, its speed will____________?
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A. increases

B. none of the above

C. the field winding resistance of a DC shunt motor is increases, its speed will

D. remains same

E. decreases

23. Which one of the following is not the function of pole shoes in a D.C. machine ?
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A. To reduce eddy current loss

B. To reduce the reluctance of the magnetic path

C. To spread out flux for better uniformity

D. To support the field coils

24. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be______________?
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A. around 90%

B. anywhere between 75% and 90%

C. less than 50%

D. 100%

25. Regenerative method of braking is based on that___________?
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A. none of the above

B. back e.m.f. of rotor is more than the applied voltage

C. back e.m.f. is less than the applied voltage

D. back e.m.f. is equal to the applied voltage
26. Hopkinsons test on D.C. machines is conducted at_______________?
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A. no-load

B. full-load

C. part load

D. overload

27. Which of the following test can be performed on DC series motor?
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A. Field test

B. Hopkinson test

C. Swinburne test

D. Brake test

28. Which of the following loss in a D.C. generator is dissipated in the form of heat?
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A. Core loss

B. Mechanical loss

C. All of the above

D. Copper loss

29. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
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A. none of the above

B. 10% of the previous value

C. 100% of the previous value

D. 50% of the previous value

E. 25% of the previous value
30. The speed of a D.C. series motor is_____________?
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A. proportional to the armature current

B. proportional to field current

C. inversely proportional to the armature current

D. proportional to the square of the armature current

31. Torque developed by a D.C. motor depends upon_____________?
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A. current flow through the conductors

B. radius of armature

C. magnetic field

D. active length of the conductor

E. all above factors

F. number of conductors

32. The armature torque of the D.C. shunt motor is proportional to____________?
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A. field flux only

B. armature current only

C. both A. and B.

D. none of the above

33. Which D.C. motor is generally preferred for cranes and hoists ?
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A. Shunt motor

B. Series motor

C. Differentially compounded motor

D. Cumulatively compounded motor

34. A dc series motor should not be started on no load because it would___________?
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A. draw more current without producing sufficient torque

B. run at dangerously high speed

C. not develop starting torque

D. fail to start without load

35. In D.C. machines the residual magnetism is of the order of_________________?
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A. 10 to 15 per cent

B. 20 to 25 per cent

C. 50 to 75 per cent

D. 2 to 3 per cent
36. In a DC motor the inter-pole winding is connected in________________?
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A. parallel big field winding

B. parallel with armature winding

C. series with field winding

D. series speed armature winding
37. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
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A. High speed operation

B. Low speed operation

C. Variable speed operation

D. Fixed speed operation

38. If a D.C. motor designed for 40C ambient temperature is to be used for 50C ambient temperature, then the motor_____________?
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A. is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor

B. can be used for 50C ambient temperature also

C. of higher H.P. should be selected

D. of lower H.P. should be selected

39. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be_____________?
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A. more than full-load current

B. less than full-load current

C. almost negligible

D. rated full-load current

40. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?
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A. Hopkinsons test

B. Brake test

C. Swinburnes test

D. Field test
41. The total losses in a well designed D.C. generator of 10 kW will be nearly______________?
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A. 500 W

B. 1000 W

C. 1500 W

D. 100 W

42. Which of the following motor is preferred for operation in highly explosive atmosphere ?
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A. Series motor

B. Shunt motor

C. Air motor

D. Battery operated motor

43. Which of the following motors is usually used in house-hold refrigerators ?
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A. Reluctance motor

B. D.C. series motor

C. D.C. shunt motor

D. Single phase induction motor (split phase start or induction run motor)

E. Synchronous motor

44. Speed control by Ward Leonard method gives uniform speed variation_____________?
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A. in one direction

B. in both directions

C. below normal speed only

D. above normal speed only

45. In Ward-Leonard control the lower limit of speed is imposed by________?
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A. mechanical losses of motor and generator together

B. residual magnetism of the generator

C. all of the above

D. core losses of motor

46. Which of the following load normally needs starting torque more than the rated torque?
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A. Air compressors

B. Centrifugal pumps

C. Conveyors

D. Blowers

47. In a D.C. generator, the iron losses mainly take place in___________/
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A. armature conductors

B. armature rotor

C. commutator

D. yoke

48. The speed of a D.C. shunt motor more than its full-load speed can be obtained by_____________?
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A. increasing the field current

B. increasing the armature current

C. decreasing the field current

D. decreasing the armature current

49. Which motor has the poorest speed control?
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A. Differentially compounded motor

B. Cumulatively compounded motor

C. Shunt motor

D. Series motor
50. With the increase in temperature, the speed of DC series motor______________?
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A. decreases

B. remain same

C. none of the above

D. increases