Basic Electrical Engineering MCQ- 12

Basic Electrical Engineering MCQ- 12

21. In D.C. generators, current to the external circuit from armature is given through

(a) commutator

(b) solid connection

(c) slip rings

(d) none of above

Ans: a

23. Brushes of D.C. machines are made of

(a) carbon

(b) soft copper

(c) hard copper

(d) all of above

Ans: a

24. If B is the flux density, I the length of conductor and v the velocity of conductor, then

induced e.m.f. is given by

(a)Blv

(b)Blv2

(c)Bl2v

(d)Bl2v2

Ans: a

25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen

coils, the pole pitch will be

(a) 4

(b) 8

(c) 16

(d) 32

Ans: b

26. The material for commutator brushes is generally

(a) mica

(b) copper

(c) cast iron

(d) carbon

Ans: d

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

(a) graphite

(b) paper

(c) mica

(d) insulating varnish

Ans: c

28. 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

Ans: c

29. 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 magnetisation

(c) crossmagnetisation as well as demagnetising

(d) cross magnetisation only

Ans: c

30. Armature reaction of an unsaturated D.C. machine is

(a) crossmagnetising

(b) demagnetising

(c) magnetising

(d) none of above

Ans: a