DC Generator Objective Type Question Answer

1. The yoke of a d.c. machine is made of

(i) silicon steel
(ii) soft iron
(iii) aluminium
(iv) cast steel

2. The armature of a d.c. machine is made of

(i) silicon steel
(ii) wrought iron
(iii) cast steel
(iv) soft iron

3. The coupling field between electrical and mechanical systems of a d.c. machine is …….

(i) electric field
(ii) magnetic field
(iii) both electric and magnetic fields
(iv) none of the above

4. The real working part of a d.c. machine is

(i) commutator
(ii) field winding
(iii) armature winding
(iv) none of the above

5. …….. d.c. machines are most common.

(i) 2-pole
(ii) 4-pole
(iii) 6-pole
(iv) 8-pole

6. The armature winding of a d.c. machine is placed on the rotor to

(i) save iron
(ii) reduce losses
(iii) facilitate commutation
(iv) reduce armature reaction

7. The yoke of a d.c. machine carries ……. pole flux.

(i) the
(ii) one-half of
(iii) two times the
(iv) none of the above

8. A 4-pole d.c. machine has ……. magnetic circuits.

(i) 2
(ii) 8
(iii) 4
(iv) none of the above

9. The field structure of a d.c. machine uses

(i) salient-pole
(ii) non-salient pole arrangement arrangement
(iii) both (i) and (ii)
(iv) none of the above

10. Small d.c. machines generally have poles

(i) 4
(ii) 6
(iii) 2
(iv) 8

11. The annature of a d.c. machine is laminated in order to reduce

(i) eddy current loss
(ii) hysteresis loss
(iii) copper loss
(iv) frictional loss

12. The current in armature conductors of a d.c. machine is

(i) pure d.c.
(ii) pulsating d.c.
(iii) a. c.
(iv) pure d.c. plus pulsating d.c.

13. The greatest eddy current loss occurs in the ……… of a d.c. machine.

(i) field poles
(ii) yoke
(iii) commutator
(iv) armature poles

14. The brush voltage drop in a d.c. machine is about

(i) 0.1 V
(ii) 10 V
(iii) 2 V
(iv) 20 V

15. Carbon brushes are used in a d.c. machine because

(i) carbon lubricates and polishes the commutator
(ii) contact resistance is decreased
(iii) carbon is cheap
(iv) none of the above

16. The armature winding of a d.c. machine is ….. winding.

(i) an open-circuit
(ii) a closed-circuit
(iii) partly open-circuit and partly closed-circuit
(iv) none of the above

17. The commutator pitch for a simplex lap winding is equal to

(i) number of poles of the machine
(ii) pole pairs
(iii) 1
(iv) none of the above

18. In a simplex wave winding, the number of parallel paths is equal to

(i) number of poles in the machine
(ii) 2
(iii) number of pairs of poles
(iv) none of the above

19. The number of parallel paths in a simplex lap winding is equal to

(i) 2
(ii) number of pairs of poles
(iii) number of poles
(iv) none of the above

20. The relation among commutator pitch (Y_c), front pitch (Y_f) and back pitch (Y_b) is ………

(i) Y_c = algebraic sum of Y_f and Y_b
(ii) Y_c = algebraic difference of V_f and Y_b
(iii) Y_c = Y_b/Y_f
(iv) none of the above