DC Machine Objective Type Questions with Answer of Previous Year Exam asked Questions.

Electrical Engineering Objective Questions and Answer (MCQ)- DC Machine Competitive questions

For electrical engineer DC Machine is one of best and important chapter for competitive exam point of view. We have published a list of  50 Objective type Questions from DC Machine which is very useful in objectives type of paper. Answer key of objective questions is also provided at last paragraph of the page. For more objectives questions of Electrical click the below link





List of Multiple Choice Questions Objective type Electrical Machines D.C. Motor Questions with Answer - 


1. In a d.c. motor, unidirectional torque is produced with the
help of
(a) brushes
(b) commutator
(c) end-plates
(d) both (a) and (b)

2. The counter e.m.f. of a d.c. motor
(a) often exceeds the supply voltage
(b) aids the applied voltage
(c) helps in energy conversion
(d) regulates its armature voltage

3. The normal value of the armature resistance of a d.c.
motor is
(a) 0.005
(b) 0.5
(c) 10
(d) 100

4. The Eb/V ratio of a d.c. motor is an indication of its
(a) efficiency
(b) speed regulation
(c) starting torque
(d) Running Torque

5. The mechanical power developed by the armature of a
d.c. motor is equal to
(a) armature current multiplied by back e.m.f.
(b) power input minus losses
(c) power output multiplied by efficiency
(d) power output plus iron losses

6. The induced e.m.f. in the armature conductors of a d.c.
motor is
(a) sinusoidal
(b) trapezoidal
(c) rectangular
(d) alternating

7. A d.c. motor can be looked upon as d.c. generator with
the power flow
(a) reduced
(b) reversed
(c) increased
(d) modified

8. In a d.c. motor, the mechanical output power actually
comes from
(a) field system
(b) air-gap flux
(c) back e.m.f.
(d) electrical input power

9. The maximum torque of d.c. motors is limited by
(a) commutation
(b) heating
(c) speed
(d) armature current

10. Which of the following quantity maintains the same
direction whether a d.c. machine runs as a generator or as
a motor ?
(a) induced e.m.f.
(b) armature current
(c) field current
(d) supply current

11. Under constant load conditions, the speed of a d.c.
motor is affected by
(a) field flux
(b) armature current
(c) back e.m.f.
(d) both (b) and (c)

12. It is possible to increase the field flux and, at the same
time, increase the speed of a d.c. motor provided its
.......... is held constant.
(a) applied voltage
(b) torque
(c) Armature circuit resistance
(d) armature current

13. The current drawn by a 120 - V d.c. motor of armature
resistance 0.5 Ω and back e.m.f. 110 V is .......... ampere.
(a) 20
(b) 240
(c) 220
(d) 5

14. The shaft torque of a d.c. motor is less than its
armature torque because of .......... losses.
(a) copper
(b) mechanical
(c) iron
(d) rotational

15. A d.c. motor develops a torque of 200 N-m at 25 rps. At
20 rps it will develop a torque of
.......... N-m.
(a) 200
(b) 160
(c) 250
(d) 128

16. Neglecting saturation, if current taken by a series motor
is increased from 10 A to 12 A, the percentage increase in
its torque is ........ percent
(a) 20
(b) 44
(c) 30.5
(d) 16.6

17. If load on a d.c. shunt motor is increased, its speed is
decreased due primarily to
(a) increase in its flux
(b) decrease in back e.m.f.
(c) increase in armature current
(d) increase in brush drop

18. If the load current and flux of a d.c. motor are held
constant and voltage applied across its
armature is increased by 10 per cent, its speed will
(a) decrease by about 10 per cent
(b) remain unchanged
(c) increase by about 10 per cent
(d) increase by 20 per cent.

19. If the pole flux of a d.c. motor approaches zero, its
speed will
(a) approach zero
(b) approach infinity
(c) no change due to corresponding change in back e.m.f.
(d) approach a stable value somewhere between zero and
infinity.

20. If the field circuit of a loaded shunt motor is suddenly
opened
(a) it would race to almost infinite speed
(b) it would draw abnormally high armature current
(c) circuit breaker or fuse will open the circuit before too
much damage is done to the motor
(d) torque developed by the motor would be reduced to
zero.

21. Which of the following d.c. motor would be suitable for
drives requiring high starting torque but only fairly constant
speed such as crushers ?
(a) shunt
(b) series
(c) compound
(d) permanent magnet

22. A d.c. shunt motor is found suitable to drive fans
because they require
(a) small torque at start up
(b) large torque at high speeds
(c) practically constant voltage
(d) both (a) and (b)

23. Which of the following load would be best driven by a
d.c. compound motor ?
(a) reciprocating pump
(b) centrifugal pump
(c) electric locomotive
(d) fan

24. As the load is increased, the speed of a d.c. shunt
motor
(a) increases proportionately
(b) remains constant
(c) increases slightly
(d) reduces slightly

25. Between no-load and full-load, .......... motor develops
the least torque
(a) series
(b) shunt
(c) cumulative compound
(d) differential compound

26. The Ta/Ia graph of a d.c. series motor is a
(a) parabola from no-load to overload
(b) straight line throughout
(c) parabola throughout
(d) parabola upto full-load and a straight line at overloads.

27. As compared to shunt and compound motors, series
motor has the highest torque because of its comparatively
.......... at the start.
(a) lower armature resistance
(b) stronger series field
(c) fewer series turns
(d) larger armature current

28. Unlike a shunt motor, it is difficult for a series motor to
stall under heavy loading because
(a) it develops high overload torque
(b) its flux remains constant
(c) it slows down considerably
(d) its back e.m.f. is reduced to almost zero.

29. When load is removed, .......... motor will run at the
highest speed.
(a) shunt
(b) cumulative-compound
(c) differential compound
(d) series

30. A series motor is best suited for driving
(a) lathes
(b) cranes and hoists
(c) shears and punches
(d) machine tools

31. A 220 V shunt motor develops a torque of 54 N-m at
armature current of 10 A. The torque produced when the
armature current is 20 A, is
(a) 54 N-m
(b) 81 N-m
(c) 108 N-m
(d) None of the above

32. The d.c. series motor should never be switched on at no
load because
(a) the field current is zero
(b) The machine does not pick up
(c) The speed becomes dangerously high
(d) It will take too long to accelerate.

33. A shunt d.c. motor works on a.c. mains
(a) unsatisfactorily
(b) satisfactorily
(c) not at all
(d) none of the above

34. A 200 V, 10 A motor could be rewound for 100 V, 20 A
by using .......... as many turns per coil of wire, having
.......... the cross-sectional area.
(a) twice, half
(b) thrice, one third
(c) half, twice
(d) four times, one-fourth


Answers Key
1. (d) 2. (c) 3.(b) 4. (a) 5. (a) 6. (a)    7. (b)    8. (d)
9. (a) 10. (a)
11. (a) 12. (d) 13. (a) 14. (d) 15. (c) 16. (b) 17. (b) 18. (c)
19. (b) 20. (c)
21. (c) 22. (d) 23. (a) 24. (d) 25. (a) 26. (d) 27. (b) 28. (a)
29. (d) 30. (b)
31. (c) 32. (c) 33. (a) 34. (c).

If you have any doubt in any questions than you are most welcome to comment.

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