Rotating Magnetic Field in 3 phase induction motor - MCQs with Answers

Rotating Magnetic Field in 3 phase induction motor- MCQs with Answers

Q1. In a three phase induction motor, the resultant of three alternating fluxes, separated from each other by 120 degree has constant amplitude

a. Equal to the maximum amplitude of an individual flux
b. Twice of the maximum amplitude of an individual flux
c. 1.5 times of the maximum amplitude of an individual flux
d. All of these

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Q2. If the frequency of a three phase induction motor is doubled and number of poles is halved, then its synchronous speed is given by

a. Remains same
b. Becomes double of the original synchronous speed
c. Becomes four times of the original synchronous speed
d. Becomes half of the original synchronous speed.

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Q3. A three phase 4 pole, induction motor is supplied from 50 Hz supply. Then its synchronous speed will be

a. 1000 rpm
b. 1500 rpm
c. 1600 rpm
d. 2000 rpm

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Q4. In a three phase induction motor, the direction of rotation of rotating magnetic field can be reversed by

a. Interchanging any two terminals of three phase winding while connecting it to ac supply
b. by reversing the direction of rotating magnetic field
c. Cannot be changed
d. None of these

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Q5. For connecting the rotating member of machine to the external stationary circuit,

a. Slip rings and brush assembly is used
b. Only slip ring is used
c. Only brushes are used
d. Directly connected to the external stationary circuit

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Q6. If the air gap of the induction motor increases then its power factor will

a. Increase
b. Decreases
c. Remains same
d. Either increases or decreases

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Q7. When the air gap is smaller in induction motor then its

a. magnetizing current reduces
b. starting torque increases
c. both a and b
d. neither a nor b

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