1. .In a D.C. shunt motorspeed is
A. independent of armature current
B. directly proportional to the armature current
C. proportional to the square of the current
D. inversely proportional to the armature current
Correct Option: independent of armature current
2. The type of D.C. motor used for shears and punches is
A. shunt motor
B. series motor
C. differential compoutid D.C. motor
D. cumulative compound D.C. motor
Correct Option: cumulative compound D.C. motor
3. If a D.C. motor is connected across the A.C. supply it will
A. run at normal speed
B. not run
C. run at lower speed
D. burn due to heat produced in the field winding by .eddy currents
Correct Option: burn due to heat produced in the field winding by .eddy currents
4. .In a D.C. shunt motorunder the conditions of maximum powerthe current in the armature will be
A. almost negligible
B. rated full-load current
C. less than full-load current
D. more than full-load current
Correct Option: more than full-load current
5. Differentially compound D.C. motors can find applications requiring
A. high starting torque
B. low starting torque
C. variable speed
D. frequent on-off cycles
Correct Option: low starting torque
6. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
A. decreasing the field current
B. increasing the field current
C. decreasing the armature current
D. increasing the armature current
Correct Option: decreasing the field current
7. .A direct on line starter is used: for starting motors
A. iip to 5 H.P.
B. up to 10 H.P.
C. up to 15 H.P.
D. up to 20 H.P.
Correct Option: iip to 5 H.P.
8. By looking at which part of the motorit can be easily confirmed that a particular motor is D.C. motor?
A. Frame
B. Shaft
C. Commutator
D. Stator
Correct Option: Commutator
9. These days D.C. motors are widely used in
A. pumping sets
B. air compressors
C. electric traction
D. machine shops
Correct Option: electric traction
10. To get the speed of D.Cmotor below the normal without wastage of electrical energy is used.
A. Ward Leonard control
B. rheostatic control
C. any of the above method
D. none of the above method
Correct Option: Ward Leonard control
11. .In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
A. back e.m.f. is equal to armature drop
B. armature drop is negligible
C. flux is proportional to armature current
D. flux is practically constant in D:C. shunt motors
Correct Option: flux is practically constant in D:C. shunt motors
12. A D.C. series motor is that which
A. has its field winding consisting of thick wire and less turns
B. has a poor torque
C. can be started easily without load
D. has almost constant speed
Correct Option: has its field winding consisting of thick wire and less turns
13. When two D.C. series motors are connected in parallelthe resultant speed is
A. more than the normal speed
B. loss than the normal speed
C. normal speed
D. zero
Correct Option: zero
14. If a D.C. motor is to be selected for conveyorswhich rriotor would be preferred ?
A. Series motor
B. Shunt motor
C. Differentially compound motor
D. Cumulative compound motor
Correct Option: Series motor
15. Starters are used with D.C. motors because
A. these motors have high starting torque
B. these motors are not self-starting
C. back e.m.f. of these motors is zero initially
D. to restrict armature current as there is no back e.m.f. while starting
Correct Option: to restrict armature current as there is no back e.m.f. while starting
16. Which D.C. motor will be preferred for machine tools ?
A. Series motor
B. Shunt motor
C. Cumulative compound motor
D. Differential compound motor
Correct Option: Shunt motor
17. The direction of rotation of a D.C. series motor can be changed by
A. interchanging supply terminals
B. interchanging field terminals
C. either of (a) and (b) above
D. None of the above
Correct Option: interchanging field terminals
18. Which of the following application requires high starting torque ?
A. Lathe machine
B. Centrifugal pump
C. Locomotive
D. Air blower
Correct Option: Locomotive
19. For starting a D.C. motor a starter is required because
A. it limits the speed of the motor
B. it limits the starting current to a safe value
C. it starts the motor
D. none of the above
Correct Option: it limits the starting current to a safe value
20. Which D.C. motor is preferred for elevators ?
A. Shunt motor
B. Series motor
C. Differential compound motor
D. Cumulative compound motor
Correct Option: Cumulative compound motor
21. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
A. The motor will stop
B. The motor will continue to run
C. The armature may burn
D. The motor will run noisy
Correct Option: The armature may burn
22. In D.C. shunt motors as load is reduced
A. the speed will increase abruptly
B. the speed will increase in proportion to reduction in load
C. the speed will remain almost/constant
D. the speed will reduce
Correct Option: the speed will remain almost/constant
23. .The current drawn by the armature of D.C. motor is directly proportional to
A. the torque required
B. the speed of the motor
C. the voltage across the terminals
D. none of the above
Correct Option: the torque required
24. The power mentioned on the name plate of an electric motor indicates
A. the power drawn in kW
B. the power drawn in kVA
C. the gross power
D. the output power available at the shaft
Correct Option: the output power available at the shaft
25. The speed of a D.C. series motor is
A. proportional to the armature current
B. proportional to the square of the armature current
C. proportional to field current
D. inversely proportional to the armature current
Correct Option: inversely proportional to the armature current
26. The ratio of starting torque to full-load torque is least in case of
A. series motors
B. shunt motor
C. compound motors
D. none of the above
Correct Option: shunt motor
27. In D.C. motor which of the following can sustain the maximum temperature rise?
A. Slip rings
B. Commutator
C. Field winding
D. Armature winding
Correct Option: Field winding
28. .The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
Correct Option: 0.5
29. The condition for maximum power in case of D.C. motor is
A. back e.m.f. = 2 x supply voltage
B. back e.m.f. = | x supply voltage
C. supply voltage = | x back e.m.f.
D. supply voltage = back e.m.f.
Correct Option: back e.m.f. = | x supply voltage
30. In D.C. machines fractional pitch winding is used
A. to improve cooling
B. to reduce copper losses
C. to increase the generated e.m.f.
D. to reduce the sparking
Correct Option: to reduce the sparking
31. The starting resistance of a D.C. motor is generally
A. low
B. around 500 Q
C. 1000 Q
D. infinitely large
Correct Option: low
32. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
A. Series motor
B. Shunt motor
C. Cumulatively compounded motor
D. Differentially compounded motor
Correct Option: Cumulatively compounded motor
33. In a D.C. series motorif the armature current is reduced by 50%the torque of the motor will be equal to
A. 100% of the previous value
B. 50% of the previous value
C. 25% of the previous value
D. 10% of the previous value
Correct Option: 25% of the previous value
34. In case-the conditions for maximum power for a D.C. motor are establishedthe efficiency of the motor will be
A. 100%
B. around 90%
C. anywhere between 75% and 90%
D. less than 50%
Correct Option: less than 50%
35. In case of conductively compensated D.C. series motorsthe compensating winding is provided
A. as separately wound unit
B. in parallel with armature winding
C. in series with armature winding
D. in parallel with field winding
Correct Option: in series with armature winding
36. Which of the following load normally needs starting torque more than the rated torque?
A. Blowers
B. Conveyors
C. Air compressors
D. Centrifugal pumps
Correct Option: Conveyors
37. A three point starter is considered suitable for
A. shunt motors
B. shunt as well as compound motors
C. shuntcompound and series motors
D. all D.C. motors
Correct Option: shunt as well as compound motors
38. If the supply voltage for a D.C. motor is increasedwhich of the following will decrease ?
A. Starting torque
B. Operating speed
C. Full-load current
D. All of the above
Correct Option: Full-load current
39. .Which one of the following is not the function of pole shoes in a D.C. machine ?
A. To reduce eddy current loss
B. To support the field coils
C. To spread out flux for better unifor-mity
D. To reduce the reluctance of the mag-netic path
Correct Option: To reduce eddy current loss
40. Which of the following motor is preferred for operation in highly explosive atmosphere ?
A. Series motor
B. Shunt motor
C. Air motor
D. Battery operated motor
Correct Option: Air motor
41. Sparking at the commutator of a D.C. motor may result in
A. damage to commutator segments
B. damage to commutator insulation
C. increased power consumption
D. all of the above
Correct Option: all of the above
42. .Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
A. Voltage control method
B. Field control method
C. Armature control method
D. All above methods
Correct Option: Armature control method
43. Sparkingis discouraged in a D.C. motor because
A. it increases the input power con
B. commutator gets damaged
C. both (a) and (b)
D. none of the above
Correct Option: commutator gets damaged
44. The speed of a D.C. motor can be varied by varying
A. field current
B. applied voltage
C. resistance in series with armature
D. any of the above
Correct Option: resistance in series with armature
45. .If I2 be the armature currentthen speed of a D.C. shunt motor isindependent of Ia
A. independent of Ia
B. proportional to la
C. varies as (Ia)
D. varies as la
Correct Option: independent of Ia
46. Which D.C. motor is generally preferred for cranes and hoists ?
A. Series motor
B. Shunt motor
C. Cumulatively compounded motor
D. Differentially compounded motor
Correct Option: Series motor
47. Speed control by Ward Leonard method gives uniform speed variation
A. in one direction
B. in both directions
C. below normal speed only
D. above normal speed only.
Correct Option: in both directions