# Practice Test: Question Set - 12

1. Regenerative method of braking is based on that
(A) Back e.m.f. is less than the applied voltage
(B) Back e.m.f. is equal to the applied voltage
(C) Back e.m.f. of rotor is more than the applied voltage
(D) None of the above

2. Which of the following method of speed control of D.C. machine will offer minimum efficiency?
(A) Voltage control method
(B) Field control method
(C) Armature control method
(D) All above methods

3. In a D.C. generator, the iron losses mainly take place in
(A) Yoke
(B) Commutator
(C) Armature conductors
(D) Armature rotor

4. Starters are used with D.C. motors because
(A) These motors have high starting torque
(B) These motors are not self-starting
(C) Back e.m.f. of these motors is zero initially
(D) To restrict armature current as there is no back e.m.f. while starting

5. When two D.C. series motors are connected in parallel, the resultant speed is
(A) More than the normal speed
(B) Loss than the normal speed
(C) Normal speed
(D) Zero

6. A direct on line starter is used: for starting motors
(A) Up to 5 H.P.
(B) Up to 10 H.P.
(C) Up to 15 H.P.
(D) Up to 20 H.P.

7. In D.C. machines fractional pitch winding is used
(A) To improve cooling
(B) To reduce copper losses
(C) To increase the generated e.m.f.
(D) To reduce the sparking

8. The speed of a D.C. series motor is
(A) Proportional to the armature current
(B) Proportional to the square of the armature current
(C) Proportional to field current
(D) Inversely proportional to the armature current

9. In case of conductively compensated D.C. series motors, the compensating winding is provided
(A) As separately wound unit
(B) In parallel with armature winding
(C) In series with armature winding
(D) In parallel with field winding

10. Three point starter can be used for
(A) Series motor only
(B) Shunt motor only
(C) Compound motor only
(D) Both shunt and compound motor

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