Polyphase Induction Motors Objective Questions - Set 01 - ObjectiveBooks

# Practice Test: Question Set - 01

1. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor?
(A) By changing the number of stator poles
(B) Rotor rheostat control
(C) By operating two motors in cascade
(D) By injecting e.m.f. in the rotor circuit

2. Step-less speed control of induction motor is possible by which of the following methods?
(A) e.m.f. injection in rotor eueuit
(B) Changing the number of poles
(D) None of the above

3. In a three-phase induction motor, the number of poles in the rotor winding is always
(A) Zero
(B) More than the number of poles in stator
(C) Less than number of poles in stator
(D) Equal to number of poles in stator

4. Slip of an induction motor is negative when
(A) Magnetic field and rotor rotate in opposite direction
(B) Rotor speed is less than the synchronous speed of the field and are in the same direction
(C) Rotor speed is more than the synchronous speed of the field and are in the same direction
(D) None of the above

5. As load on an induction motor goes on increasing
(A) Its power factor goes on decreasing
(B) Its power factor remains constant
(C) Its power factor goes on increasing even after full load
(D) Its power factor goes on increasing up to full load and then it falls again

6. A 3-phase slip ring motor has
(A) Double cage rotor
(B) Wound rotor
(C) Short-circuited rotor
(D) Any of the above

7. In a three-phase induction motor
(A) Power factor at starting is high as compared to that while running
(B) Power factor at starting is low as compared to that while running
(C) Power factor at starting in the same as that while running
(D) None of these

8. The complete circle diagram of induction motor can be drawn with the help of data found from
(B) Blocked rotor test
(C) Stator resistance test
(D) All of the above

9. An induction motor can run at synchronous speed when
(A) It is run on load
(B) It is run in reverse direction
(C) It is run on voltage higher than the rated voltage
(D) e.m.f. is injected in the rotor circuit

10. Insertion of resistance in the rotor of an induction motor to develop a given torque
(A) Decreases the rotor current
(B) Increases the rotor current
(C) Rotor current becomes zero
(D) Rotor current remains same

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