Sunday, April 22, 2012

Induction Motor Objective Questions Answers 3

1. In an induction motor air gap is increased:
a) speed will reduce
b) efficiency will improve
c) power factor will be lowered
d) breakdown torque will reduce

2. In circle diagram of an induction motor the diameter of the circle represent:
a) rotor current
b) line voltage
c) operating torque
d) maximum torque

When a poly phase induction motor loaded:
a) motor speed decreases
b) stator flux cuts the rotor bars more rapidly
c) emf induced in the rotor and rotor frequency increases
d) all the above

3. Torque slip characteristics of an induction motor is approximately an:
a) hyperbola
b) rectangular parabola
c) parabola
d) rectangular hyperbola

4. In an induction motor air gap flux density is kept low so as to:
a) improve efficiency
b) improve power factor
c) improve maximum torque
d) both (a) and (b)

5. The relative speed between stator and rotor fluxes is equal to:
a) Synchronous speed Ns
b) Rotor speed N
c) Zero
d) Ns-N

6. Uneven gap in an induction motor is likely to cause:
a) heating of the motor
b) unbalancing of the shaft
c) both (a) and (b)
d) none of the above

7. The squirrel cage rotor of a 6-pole induction motor can be used for __ induction motor:
a) only 6 pole
b) 6 pole or 12 pole
c) any number of even number of poles
d) none of the above

8. The rotor of a 3 phase induction motor rotates in the same direction of that of the stator rotating field. This can be explained by:
a) Faraday's law of electromagnetic induction
b) Lenz's law
c) Newtons law of motion
d) Flemings right law

9. The value of the airgap flux density in an induction motor is in the range of:
a) 0.35 to 0.6T
b) 0.8 to 1.0 T
c) 0.1 to 0.25T
d) 2.5 to 3.5 T

10. The stator core of the induction motor is laminated in order to reduce:
a) Eddy current loss
b) Hysteresis loss
c) both (a) and (b)
d) none of the above