Class Room Quiz

Induction Motor Class_26/10/2026

Class Room Quiz

An induction motor primarily works on the principle of:

1: An induction motor primarily works on the principle of:

Electrostatic fields attraction and repulsions

Amperes Law

Magnetic Locking of stator and rotor magnetic fields

Magnetic fields attraction and repulsions due to mutual induction

The synchronous speed of a 4-pole, 50 Hz induction motor is:

2: The synchronous speed of a 4-pole, 50 Hz induction motor is:

1500 rpm

750 rpm

1000 rpm

3000 rpm

Which expression gives the slip of an induction motor? (Ns: synchronous speed; Nr: rotor speed.)

3: Which expression gives the slip of an induction motor? (Ns: synchronous speed; Nr: rotor speed.)

s = (Ns + Nr)/Ns

s = (Ns − Nr)/Nr

s = (Ns − Nr)/Ns

s = Ns/Nr

Rotor current is induced when there is

4: Rotor current is induced when there is

Equal rotor and synchronous speeds

A direct electrical connection between stator and rotor

Relative motion between the rotor and the stator magnetic field

DC supply connected to the rotor

Why are squirrel-cage rotor bars commonly skewed

5: Why are squirrel-cage rotor bars commonly skewed

To increase the supply frequency

To increase the number of poles

To eliminate rotor copper losses

To reduce magnetic locking, noise, and torque pulsations

What is the peak magnitude of the flux density (Bm) swing in the cycle of sine wave excitation with respect to the BH Curve?

6: What is the peak magnitude of the flux density (Bm) swing in the cycle of sine wave excitation with respect to the BH Curve?

2Bm

4Bm

Bm

0.5Bm

The main purpose of maintaining approximately constant V/f below base speed is to:

7: The main purpose of maintaining approximately constant V/f below base speed is to:

Keep the rotor speed exactly constant

Maintain approximately constant air-gap flux

Eliminate all motor losses

Keep slip equal to zero

At no load, an induction motor draws current mainly to:

8: At no load, an induction motor draws current mainly to:

Establish the magnetic field and supply its losses

Eliminate the rotor resistance

Produce rated shaft torque

Make the rotor exceed synchronous speed

An induction motor operates on a 50 Hz supply with a slip of 4%. What is the rotor current frequency?

9: An induction motor operates on a 50 Hz supply with a slip of 4%. What is the rotor current frequency?

50 Hz

2 Hz

20 Hz

4 Hz

A uniform flux density of 0.5 T acts normally over an area of 0.02 m². What is the magnetic flux?

10: A uniform flux density of 0.5 T acts normally over an area of 0.02 m². What is the magnetic flux?

0.01 Wb

0.001 Wb

0.1 Wb

1 Wb