DC MACHINES-MCQ

1. Lamintions of core are generally made of

A. cast iron
B. carbon
C. stainless steel
D. silicon steel

Ans: D

2. The armature of DC generator is laminated to

A. reduce the bulk
B. provide passage for cooling air
C. insulate the core
D. reduce eddy current loss

Ans: D

3.The field coils of DC generator are usually made of

A. mica
B. copper
C. cast iron
D. carbon

Ans: B

4. In lap winding the number of brushes is always

A.two
B. double the number of poles
C. equal to number of poles
D. half the number of poles

Ans: C

5. The insulating material used between the commutator segments is normally

A. varnish
B. mica
C. graphite
D. paper

Ans: B

6.For generating large currents on DC generators which winding is generally preferred ?

A. lap winding
B. progressive wave winding
C. retrogressive wave winding
D. current depends on design

Ans: A

7.The number of commutator segments is

A. equals to no of coils
B. less than number of coils
C. double the number of coils
d.none of these

Ans: A

8. In a dc generator, the effect of armature reaction on the main pole is to

A. reduce it
B. distort it
C. reverse it
D. both (a) and (b)

Ans: D

9. Which dc motor is generally preferred for cranes and hoists ?

a. series motor
b. shunt motor
c. cumulatively compound motor
d. differentially compound motor

Ans: a

10. When load is removed .......... motor willrun at highest speed

a. shunt
b. cummulative compound
c. differential compound
d. series

Ans: d

11. which of the following law/rule can be used to determine the direction of rotation of dc motor ?

a. lenz law
b. faradays law
c. coloumbs law
d. flemigs left hand rule

Ans:  d

12. By looking at which part of the motor, it can be easily confirmed that a particular motor is DCmotor ?

a. frame
b. shaft
c. commutator
d. stator

Ans: c

13. Lap winding is suitable for ........ current............. voltage dc generators

a. high, low
b. low, high
c. low, low
d. high, high

Ans : B

14. The induced voltage across a coil with 250 turns that is located in a magnetic field that is changing at a rate of 8 Wb/s is

A. 1,000 V
B. 2,000 V
C. 31.25 V
D. 3,125 V

Ans: B

15. A 50 HZ alternator will run at the greatest possible speed if it is wound for ...... poles

A. 8
B. 6
C. 4
D. 2

Ans: D

16. The unit for reluctance is

A. tesla 
B. At/Wb
C. At/m 
D. Wb

Ans: B

17. In a 6 pole dc machine,90 mechanical degrees corresponds to ......... electrical degrees.

A. 30
B. 180
C. 45
D. 270

Ans: D

18. The sole purpose of commutator in a dc generator is to.......

A. increase output voltage
B. reduce sparking at brushes
C. provide smoother output
D. convert induced ac in to dc

Ans: D

19. permeability is reciprocal of 

A.reluctivity
B.susceptibility
C.permittivity
D.conductivity

Ans: A

20. In lap winding, the number of brushes is always

A. double the no.of poles
B. same as no.of poles
C. half the no.of poles
D. two.

Ans: B