Electrical and Electronics Engineering solved MCQs

1 of 13

1. With the increase in the speed of a dc motor:

a. both back emf as well as line current increases

B. both back emf and line current falls

c. back emf increases but the line current falls

d. back emf falls and line current increases

2. The output indicated on the name plate of any motor is always the:

a. gross power

B. power drawn in volt amperes

c. power drawn in watts

d. output power at the shaft

3. The direction of rotation of dc shunt motor can be reversed by interchanging:

a. the supply terminals

B. the field terminals

c. the armature terminals only

d. either field or armature terminals

4. The output power of any electrical motor is taken from the:

a. armature

B. field

c. coupling mounted on the shaft

d. motor frame

5. If the back emf in a dc motor varnishes suddenly, then the motor:

a. run at very high speeds

B. start hunting

c. burn

d. come to stall

6. The direction of the armature current in a dc motor is:

a. the same as the generated emf

B. opposite to that of generated emf

c. not dependent upon the direction of the armature emf

d. none of the above

7. When a dc machine is connected to the dc supply main it will produce:

a. emf in opposition to the applied voltage

B. emf in phase with the applied voltage

c. emf decreases with time

d. none of the above

8. The direction of rotation of a dc motor can be determined by:

a. fleming\s right hand rule

B. fleming\s left hand rule

c. lenz\s law

d. ampere\s law

9. A thick wire is used in dc series motor field winding than that in dc shunt motor:

a. to create more flux

B. to reduce the resistance

c. to carry large load current

d. both (b) and ©

10. An electrical train employing a dc series motor is running at the fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in:

a. drop in the speed and rise in the current

B. rise in the speed and drop in the current

c. rise in the speed and rise in the current

d. drop in speed with current unaltered

11. A DC shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will:

a. remains unchanged

B. increases

c. decreases

d. be zero

12. A DC series motor is best suited for electrical traction because:

a. it develops high starting torque

B. it runs at very high speed

c. it is cheaper in cost

d. it is more rugged in construction like induction motor

13. Which of the following dc motor has maximum self relieving property:

a. shunt

B. series

c. cumulative compound

d. differential compound

14. When the direction of power flow in a differential compounded motor reverses, it will operate as a:

a. cumulative compound generator

B. differential compound generator

c. series motor

d. shunt motor

15. A flywheel is employed with a dc compound motor to reduce the peak demand, the compound motor should be:

a. level compound

B. differential compound

c. cumulative compound

d. none of the above

16. The output voltage of a DC generator is

a. e = v + iara

B. e = v – iara

c. e = v + ia

d. e = v + ra

17. The material used for commutator brushes is mostly

a. copper

B. carbon

c. mica

d. cast iron

18. A 4 pole DC generator rotates at 1500 rpm. How many times in a second, will the emf induced in each armature conductor changes its direction?

a. 750

B. 100

c. 500

d. 200

19. Magnetic field of a DC generator is produced by what?

a. permanent magnets

B. electromagnets

c. both option b & c

d. none of the options

20. In a DC generator the emf generated by the armature is maximum when

a. rate of change of flux is maximum

B. rate of change of flux is minimum

c. induced voltage is high

d. shaft rotation is high

21. What is the actual arrangement of series wound generator?

a. armature and field both are parallel

B. armature and field both are connected

c. increase the speed of shaft rotation

d. armature and field both are in series with the load

22. What is the effect of armature reaction?

a. armature flux weakens the main field flux

B. armature flux distorts the main field flux

c. both option b & a

d. none of the options

23. In DC machine, brushes are always placed along

a. magnetic neutral axis

B. geometrical neutral axis

c. armature axis

d. load axis

24. What type of connection is made in between the interpole & the field winding?

a. series

B. parallel

c. compound

d. none of the options

25. In DC machine, lap winding is used in

a. high current and low voltage applications

B. high voltage and low current applications

c. where constant speed is required

d. where greater load is connected

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