Electrical MCQ -Induction motor 1-1

Induction Motor 1-1

1).A 4 pole 50 Hz induction motor is running at 1470 rpm. the frequency of rotor current is
a)    50 Hz
b)    5 Hz
c)    1 Hz
d)    0 Hz

2).When maximum starting torque is obtained,rotor power is
a)    unity
b)    zero
c)    0.707 lagging   
d)    0.5 lagging  

3).The speed of rotating magnetic field of 8 pole 50 Hz induction motor is.
a)    3000    
b)    1500
c)    1000
d)    750

4).The condition for maximum running torque is .
a)    R=X   
b)    R=S.X
c)    R=X/2
d)    R=S.X/2

5).Which of the following will vary the maximum torque?
a)    rotor resistance R  
b)    rotor reactance X
c)    both 1 and 2
d)    non of the above

6).The motor operate in stable region at which of the following slip?
a)    low slip region
b)    high slip region
c)    both 1 and 2
d)    unity slip

7).In circle diagram for induction motor, diameter of circle represents which of the following?
a)    slip.  
b)    rotor current.
c)    running torque.
d)    line voltage.

8).which of the following statement are correct
a)    the leakage reactance of the induction motor should be small
b)    a small value of leakage reactance will increase the maximum power output of motor
c)    both 1 and 2
d)    non of the above

9).As compared to an induction motor, air gap in a DC motor is
a)    Same
b)    More
c)    Less than 50%    
d)    Between 50% and 90%

10).For the speed control of polyphase squirrel cage induction motor,if frequency of operation is decreased with
a)    constant supply voltage V, starting torque Tst decreases
b)    constant V, Tst increases
c)    either of these
d)    non of the above