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1) The material for commutator brushes is generally

a) mica

b) copper

c) cast iron

d) carbon

Answer : d

2) Small d.c. machines generally have ………poles.

a) 4

b) 6

c) 2

d) 8

Answer : c

3) …….. d.c. machines are most common.

a) 2-pole

b) 4-pole

c) 6-pole

d) 8-pole

Answer : b

4) If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be

(a) demagnetisation only

(b) cross magnetisation as well as mag¬netisation

(c) crossmagnetisation as well as demagnetising

(d) cross magnetisation only

Answer : c

5) High-voltage d.c. machines use …….. winding.

a) lap

b) wave

c) either lap or wave

d) none of the above

Answer : b

6) The yoke of a d.c. machine carries ,…….. pole flux.

a) the

b) one-half of the

c) two times the

d) none of the above

Answer : b

7) The commutator pitch for a simplex lap winding is equal to …….

a) number of poles of the machine

b) pole pairs

c) 1

d) none of the above

 Answer : c

8) The greatest percentage of heat loss in a d.c. machine is due to ……….

a) eddy current loss

b) hysteresis loss

c) copper loss

d) frictional loss

Answer :c

9) The armature conductors of 6-pole, lap wound d.c. generator are divided into

a) 2 parallel paths

b) 4 parallel paths

c) 3 parallel paths

d) 6 parallel paths

Answer : d

10) Hysteresis loss in a d.c. machine is directly proportional to ……….

a) speed

b) (speed)2

c) (speed)6

d) none of the above

Answer : a

11) The greatest percentage of heat loss in a d.c. machine is due to ,……..

a) eddy current loss

b) hysteresis loss

c) copper loss

d) frictional loss

Answer : c

12) The filed winding of a d.c. shunt machine usually carries …… of the rated current of the machine.

a) 2% to 5%

b) 15 % to 20%

c) more than 20%

d) less than 0.5%

Answer : a

13) The commutator of a d.c. generator acts as

a) an amplifier

b) a rectifier

c) a load

d) none of the above

Answer : b

14) The armature copper loss in a d.c. generator is a

a) constant loss

b) variable loss

c) stray loss

d) none of the above

Answer : b

15) In D.C. generators, the brushes on commutator remain in contact with conductors which

a) lie under south pole

b) lie under north pole

c) lie under interpolar region

d) are farthest from the poles

Answer : c

16) The commutator in a d.c. machine can convert

a) a.c. to d.c.

b) d.c. to a.c.

c) both (i) and (ii)

d) none of the above

Answer : c

SOURCES :

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