1. In a 3-phase induction motor, the current is produced in the rotor conductors by
a) giving ac supply
b) giving dc supply
c) induction effect
d) pulsating dc supply
ans. c
2. When 3-phase supply is given to the stator of the motor , a
a) revolving field is set up
b) pulsating field is set up
c) revolving field at synchronous speed is set up
d) revolving field at the rotor speed is set up
ans. c
3. If any two phases of the 3-phase supply are interchanged , the motor will
a) run in the same direction
b) stop running
c) run in reverse direction
d) draw high current
ans. c
4. Different types of a 3-phase induction motors are
a) squirrel cage
b) slip-ring
c) commutator
d) all of these
ans.d
5. The rotor of a 3-phase induction motor rotates in the same direction as the direction of revolving field because of
a) Faraday's laws of electro-magnetic induction
b) Lenz's law
c) Fleming's right hand rule
d) none of these
ans. b
6. The rotor of a 3-phase induction motor always runs at
a) synchronous speed
b) less than synchronous speed
c) more than synchronous speed
d) none of these
ans. b
7. The synchronous speed of the revolving field depends upon
a) number of poles
b) supply frequency
c) flux
d) a and b are correct
ans. d
8. The frequency of induced emf in the rotor circuit is
a) maximum at stand still
b) zero at stand still
c) maximum at synchronous speed
d) none of these
ans. a
9. If one of the 3-phases of a 3-phase induction motor is disconnected while running at light load, it will
a) stop running
b) continue to run at same speed
c) run at low speed
d) run at high speed
ans. b
10. If the rotor terminals of a 3-phase slip ring induction motor are not short-circuited and the supply is given to the stator , the motor will
a) not start
b) start running
c) run at high speed
d) run at low speed
ans. a
