#MCQ_OF_ELECTRICAL_MACHINES, #OBJECTIVE_QUESTIONS_AND_ANSWERS_ELECTRICAL_MACHINES #RRB #GATE #SSC_JE #PSU #MPEB 25 Electrical Machines questions and answers focuses on all areas of Electrical Machines subject covering 20+ topics in Electrical Machines. These topics are chosen from a collection of most authoritative and best reference books on Electrical Machines. One should spend 1 hour daily for 2-3 months to learn and assimilate Electrical Machines comprehensively. This way of systematic learning will prepare anyone easily towards Electrical Machines interviews, online tests, examinations and certifications

1. ELECTRICAL MACHINE
MCQ (PART-I)
SSC(JE)/RRB/PSCProf.Prasant Tiwari

2. ELECTRICAL MACHINE
1. While comparing magnetic and electric
circuits, the flux of magnetic circuit is
compared with which parameter of
electrical circuit ?
(a) E.m.f.
(b) Current
(c) Current density
(d) Conductivity
Ans: b

3. ELECTRICAL MACHINE
2. The material for commutator brushes is
generally made
(a)mica
(b)copper
(c)cast iron
(d)carbon
Ans: d

4. ELECTRICAL MACHINE
3. A ferrite core has less eddy current loss
than an iron core because
(a) ferrites have high resistance
(b) ferrites are magnetic
(c) ferrites have low permeability
(d) ferrites have high hysteresis
Ans: a

5. ELECTRICAL MACHINE
4. Hysteresis loss least depends on
(a) volume of material
(b) frequency
(c) steinmetz coefficient of material
(d) ambient temperature
Ans: d

6. ELECTRICAL MACHINE
6. Laminated cores, in electrical machines,
are used to reduce
(a) copper loss
(b) eddy current loss
(c) hysteresis loss
(d) all of the above
Ans: b

7. ELECTRICAL MACHINE
7. The direction of rotation of a D.C. series
motor can be changed by
(a) interchanging supply terminals
(b) interchanging field terminals
(c) either of (a) and (b) above
(d) None of the above
Ans: b

8. ELECTRICAL MACHINE
8. Which of the following application
requires high starting torque ?
(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive
(d) Air blower
Ans: c TRACTION (LOCOMOTIVE) MOTOR

9. ELECTRICAL MACHINE
9. If a D.C. motor is to be selected for conveyors,
which rotor would be preferred ?
(a) Series motor
(b) Shunt motor
(c) Differentially compound motor
(d) Cumulative compound motor
Ans: a

10. ELECTRICAL MACHINE
10. Which D.C. motor will be preferred for
machine tools ?
(a) Series motor
(b) Shunt motor
(c) Cumulative compound motor
(d) Differential compound motor
Ans: b

11. ELECTRICAL MACHINE
11. Differentially compound D.C. motors
can find applications requiring
(a) high starting torque
(b) low starting torque
(c) variable speed
(d) frequent on-off cycles
Ans: b

12. ELECTRICAL MACHINE
12. Which D.C. motor is preferred for
elevators ?
(a) Shunt motor
(b) Series motor
(c) Differential compound motor
(d) Cumulative compound motor
Ans: d

13. ELECTRICAL MACHINE
13. Copper brushes in D.C. machine are
used
(a)where low voltage and high currents are involved
(b)where high voltage and small cur-rents are
involved
(c)in both of the above cases
(d)in none of the above cases
Ans: a

14. ELECTRICAL MACHINE
14. If the field of a D.C. shunt motor gets
opened while motor is running
(a) the speed of motor will be reduced by %
(b) the armature current will reduce
(c) the motor will attain dangerously high speed
(d) the motor will continue to rotate at constant speed
Ans: c

15. ELECTRICAL MACHINE
15. Starters are used with D.C. motors
because
(a) these motors have high starting torque
(b) these motors are not self-starting
(c) backe.m.f. of these motors is zero initially
(d) to restrict armature current as there is no back e.m.f.
while starting
Ans: d

16. ELECTRICAL MACHINE
16. In D.C. shunt motors as load is reduced
(a) the speed will increase abruptly
(b) the speed will increase in proportion to reduction
in load
(c) the speed will remain almost/constant
(d) the speed will reduce
Ans: c

17. ELECTRICAL MACHINE
17. A D.C. series motor is that which
(a) has its field winding consisting of thick wire and less
turns
(b) has a poor torque
(c) can be started easily without load
(d) has almost constant speed
Ans: a

18. ELECTRICAL MACHINE
18. For starting a D.C. motor a starter is
required because
(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
Ans: b

19. ELECTRICAL MACHINE
19. Laminations of core are generally
made of
(a)cast iron
(b)carbon
(c)silicon steel
(d)stainless steel
Ans: c

20. ELECTRICAL MACHINE
20. In lap winding, the number of parallel
paths are always
(a)double the number of poles
(b)same as the number of poles
(c)half the number of poles
(d)two
Ans: b

21. ELECTRICAL MACHINE
21. The armature of D.C. generator is
laminated to
(a)reduce the copper loss
(b)provide the strength
(c)insulate the core
(d)reduce eddy current loss
Ans: d

22. ELECTRICAL MACHINE
22. The resistance of armature winding
depends on
(a)length of conductor
(b)cross-sectional area of the conductor
(c)number of conductors
(d)all of the above
Ans: d

23. ELECTRICAL MACHINE
23. The field coils of D.C. generator are
usually made of
(a)mica
(b)copper
(c)cast iron
(d)carbon
Ans: b

24. ELECTRICAL MACHINE
24. The commutator segments are
connected to the armature conductors
by means of
(a)copper lugs
(b)resistance wires
(c)insulation pads
(d)brazing
Ans: a

25. ELECTRICAL MACHINE
25. In a commutator
(a)copper is harder than mica
(b)mica and copper are equally hard
(c)mica is harder than copper
(d)none of the above
Ans: c