D.C motor. Part – 2

 

11. Two D.C. Series motors are connected in series and are driving the same mechanical load. If the motors are now connected in parallel the speed become

A. one fourth

B. half

C. double

D. 4 times

12. During regenerative braking

A. The motors are disconnected from the supply

B. The motors are reverse connected to the supply

C. The motors are operated as generators

D. The motors are made to come to stand-still

13. The most inefficient method for speed control of dc motor is

A. Voltage control

B. Field control

C. Armature control

D. All of the above

14. In swineburne’s test of determination of efficiency of a dc shunt machine the no load input power supplies

A. Armature and shunt field copper losses

B. Iron losses

C. Friction and windage losses

D. All of the above

15. A 230V dc series motor is connected to a 230v ac supply

A. The motor will vibrate violently

B. The motor will run with less efficiency and more sparking

C. The motor will not run

D. The fuse will be blown

16. In the left hand rule, forefinger always represents

A. Voltage

B. Current

C. Magnetic field

D. Direction of force on the conductor

17. When the motor runs on no load, then

A. Back EMF is almost equal to applied voltage

B. Back EMF will be greater than applied voltage

C. Back EMF will be less than applied voltage

D. None of these

18. If field current is decreased in shunt dc motor, the speed of the motor

A. Remains same

B. Increases

C. Decreases

D. None of the above

19. if back e.m.f. in a d.c. motor vanishes suddenly, the motor will

a. run at very high speed

b. run at very slow speed

c. have ending burnt

d. not run at all

20. An unsaturated shunt motor runs at its rated speed when rated voltage is applied to it. If the supply voltage the motor is reduced by 25% the speed of the motor 

A. Increases by 25%

B. Remains the same

C. Decreases by 25%

D. Increases slightly