Electrical Engineering Questions - 7
Basic And Generalized Questions Are Given Below :
1. Which of the following component is usually fabricated out of silicon steel ?
(a) Bearings(b) Shaft
(c) Stator core
(d) None of the above
Ans: c
2. The frame of an induction motor is usually made of
(a) silicon steel(b) cast iron
(c) aluminum
(d) bronze
Ans: b
3. The shaft of an induction motor is made of
(a) stiff(b) flexible
(c) hollow
(d) any of the above
Ans: a
4. The shaft of an induction motor is made of
(a) high speed steel(b) stainless steel
(c) carbon steel
(d) cast iron
Ans: c
5. In an induction motor, no-load the slip is generally
(a) less than 1%(b) 1.5%
(c) 2%
(d) 4%
Ans: a
6. In medium sized induction motors, the slip is generally around
(a) 0.04%(b) 0.4%
(c) 4%
(d) 14%
Ans: c
7. In squirrel cage induction motors, the rotor slots are usually given slight skewin order to
(a) reduce wind age losses(b) reduce eddy currents
(c) reduce accumulation of dirt and dust
(d) reduce magnetic hum
Ans: d
8. In case the air gap in an induction motor is increased
(a) the magnetizing current of the rotor will decrease(b) the power factor will decrease
(c) speed of motor will increase
(d) the wind age losses will increase
Ans: b
9. Slip rings are usually made of
(a) copper(b) carbon
(c) phosphor bronze
(d) aluminum
Ans: c
10. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be
(a) 200 Hz(b) 50 Hz
(c) 2 Hz
(d) 0.2 Hz
Ans: c
11. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be
(a) Ns(b) s.N,
(c) (l-s)Ns
(d) (Ns-l)s
Ans: c
12. The efficiency of an induction motor can be expected to be nearly
(a) 60 to 90%(b) 80 to 90%
(c) 95 to 98%
(d) 99%
Ans: b
13. The number of slip rings on a squirrel cage induction motor is usually
(a) two(b) three
(c) four
(d) none
Ans: d
14. The starting torque of a squirrel-cage induction motor is
(a) low(b) negligible
(c) same as full-load torque
(d) slightly more than full-load torque
Ans: a
15. A double squirrel-cage induction motor has
(a) two rotors moving in opposite direction(b) two parallel windings in stator
(c) two parallel windings in rotor
(d) two series windings in stator
Ans: c
16. Star-delta starting of motors is not possible in case of
(a) single phase motors(b) variable speed motors
(c) low horse power motors
(d) high speed motors
Ans: a
17. The term clogging is associated with
(a) three phase transformers(b) compound generators
(c) D.C. series motors
(d) induction motors
Ans: d
18. In case of the induction motors the torque is
(a) inversely proportional to (Vslip)(b) directly proportional to (slip)2
(c) inversely proportional to slip
(d) directly proportional to slip
Ans: d
19. An induction motor with 1000 r.p.m. speed will have
(a) 8 poles(b) 6 poles
(c) 4 poles
(d) 2 poles
Ans: b
20. The good power factor of an induction motor can be achieved if the average flux density in the air gap is
(a) absent(b) small
(c) large
(d) infinity
Ans: b
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