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# DC Motor MCQ Questions And Answers

## D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

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

(a) the motor will first stop and then run in opposite direction as series motor

(b) the motor will work as series motor and run at slow speed in the same direction

(c) the motor will work as series motor and run at high speed in the same direction

(d) the motor will not work and come to stop

Ans: a

42. Which of the following motor has the poorest speed regulation?

(a) Shunt motor

(b) Series motor

(c) Differential compound motor

(d) Cumulative compound motor

Ans: b

43. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of

(a) D.C. series motor

(b) D.C. shunt motor

(c) induction motor

(d) all of above motors

Ans: a

44. As -the load is increased the speed of D.C. shunt motor will

(a) reduce slightly

(b) increase slightly

(c) increase proportionately

(d) remains unchanged

Ans: a

45. The armature torque of the D.C. shunt motor is proportional
to

(a) field flux only

(b) armature current only

(c) both (a) and (b)

(d) none of the above

Ans: b

46. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is

(a) 4.0

(b) 2.0

(c) 1.0

(d) 0.5

Ans: d

47. 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.

Ans: b

48. For which of the following applications a D.C. motor is preferred over an A.C. motor?

(a) Low speed operation

(b) High speed operation

(c) Variable speed operation

(d) Fixed speed operation

Ans: c

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

(a) 2 to 3 per cent

(6) 10 to 15 per cent

(c) 20 to 25 per cent

(d) 50 to 75 per cent

Ans: a

50. 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

Ans: a

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