1. Armature current in D.C. generators is given to the external circuit through
(A) strips.
(B) commutator.
(C) solid connection.
(D) slip rings.
Answer ⇓
2. The function of commutator in dc machine is to convert
(A) ac to dc only.
(B) dc to ac only.
(C) either ac to dc or dc to ac.
(D) none of the above.
Answer ⇓
3. Two DC generators operating in parallel must have
(A) same kW rating.
(B) same speed.
(C) the same drooping voltage characteristics.
(D) same percentage regulation.
Answer ⇓
4. Commutor segments in D.C. machine is equal to number of
(A) carbon brushes.
(B) armature coils.
(C) armature conductors.
(D) slip rings.
Answer ⇓
5. The field coils of D.C. generator are usually made of
(A) aluminium.
(B) copper.
(C) silicon steel.
(D) cast iron.
Answer ⇓
6. The nature of current flowing in the armature of a dc machine is
(A) ac.
(B) dc.
(C) pulsating.
(D) constant.
Answer ⇓
7. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by using
(A) filters.
(B) commutator with large number of segments.
(C) carbon brushes of superior quality.
(D) using equiliser rings.
Answer ⇓
8. The purpose of providing dummy coils in a generator is
(A) to reduce eddy current losses.
(B) to enhance flux density.
(C) to amplify voltage.
(D) to provide mechanical balance for the rotor.
Answer ⇓
9. The winding used in welding generator will have
(A) delta winding.
(B) lap winding.
(C) wave winding.
(D) duplex wave winding.
Answer ⇓
10. In case of D.C. machines, mechanical losses are primary function of
(A) current.
(B) voltage.
(C) speed.
(D) power factor.
Answer ⇓
11. Permeance is the reciprocal of
(A) flux density.
(B) reluctance.
(C) ampere-turns.
(D) resistance.
Answer ⇓
12. If the speed of a DC machine is doubled and the flux remains constant, the generated e.m.f.
(A) remains the same.
(B) is doubled.
(C) is halved.
(D) none of the above.
Answer ⇓
13. If the flux per pole of a shunt-wound DC generator is halved, the generated e.m.f. at constant speed
(A) is doubled.
(B) is halved.
(C) remains the same.
(D) none of the above.
Answer ⇓
14. The critical resistance of the D.C. generator is the resistance of
(A) field.
(B) brushes.
(C) armature.
(D) load.
Answer ⇓
15. If the excitation is critical, the power factor of the alternator is
(A) unity power factor.
(B) leading power factor.
(C) lagging power factor.
(D) none of the above.