In an induction motor no-load the slip is generally
less than 1%
0.015
0.02
0.04
less than 1%
Slip ring motor is recommended where
high starting torque is needed
frequent starting stopping and reversing is required
speed control is required
all above features are required
all above features are required
If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
in the opposite direction as the direction of the rotating field
in any direction depending upon phase squence of supply
in the same direction as the direction of the field
None of the above
in the same direction as the direction of the field
As load on an induction motor goes on increasing
its power factor goes on increasing up to full load and then it falls again
its power factor goes on increasing even after full load
its power factor remains constant
its power factor goes on decreasing
its power factor goes on increasing up to full load and then it falls again
In squirrel cage induction motors the rotor slots are usually given slight skew in order to
reduce magnetic hum
reduce eddy currents
reduce windage losses
reduce accumulation of dirt and dust
reduce magnetic hum
Slip rings are usually made of
aluminium
phosphor bronze
copper
carbon
phosphor bronze
A 3-phase 440 V 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be
2 Hz
200 Hz
50 Hz
0.2 Hz
2 Hz
In Ns is the synchronous speed and s the slip then actual running speed of an induction motor will be
(Ns-l)s
s.N
Ns
(l-s)Ns
(l-s)Ns
In case the air gap in an induction motor is increased
the magnetising current of the rotor will decrease
speed of motor will increase
the power factor will decrease
the windage losses will increase
the power factor will decrease
The efficiency of an induction motor can be expected to be nearly
80 to 90%
0.99
95 to 98%
60 to 90%
80 to 90%
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