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EEE :: D.C. Motors

1. The condition for maximum efficiency for a D.C. generator is

2.  A.  Eddy current losses = stray losses B.  Hysteresis losses = eddy current losses C.  Copper losses = 0 D.  Variable losses = constant losses

3. If a D.C. motor is connected across the A.C. supply it will

4.  A.  Run at normal speed B.  Not run C.  Run at lower speed D.  Burn due to heat produced in the field winding by eddy currents

5. The speed of a D.C. shunt motor can be increased by

6.  A.  Increasing the resistance in armature circuit B.  Increasing the resistance in field circuit C.  Reducing the resistance in the field circuit D.  Reducing the resistance in the armature circuit

7. The armature voltage control of D.C. motor provides

8.  A.  Constant torque drive B.  Constant voltage drive C.  Constant current drive D.  None of the above

9. Starters are used with D.C. motors because

10.  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

11. If I2 be the armature current, then speed of a D.C. shunt motor is

12.  A.  Independent of Ia B.  Proportional to Ia C.  Varies as Ia D.  None of these

13. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because

14.  A.  Back e.m.f. is equal to armature drop B.  Armature drop is negligible C.  Flux is proportional to armature current D.  Flux is practically constant in D.C. shunt motors

15. A direct on line starter is used: for starting motors

16.  A.  Up to 5 H.P. B.  Up to 10 H.P. C.  Up to 15 H.P. D.  Up to 20 H.P.

17. The ratio of starting torque to full-load torque is least in case of

18.  A.  Series motors B.  Shunt motors C.  Compound motors D.  None of the above

19. For starting a D.C. motor a starter is required because

20.  A.  It limits the speed of the motor B.  It limits the starting current to a safe value C.  It starts the motor D.  None of the above