In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be

The correct answer is C. (1 – s)Ns.

The synchronous speed of an induction motor is the speed at which the rotating magnetic field of the stator would rotate if there were no slip. The slip is the difference between the synchronous speed and the actual running speed of the motor. The actual running speed of the motor is therefore given by:

$N_a = N_s(1 – s)$

where:

• $N_a$ is the actual running speed of the motor
• $N_s$ is the synchronous speed of the motor
• $s$ is the slip

Option A is incorrect because it is the synchronous speed, not the actual running speed. Option B is incorrect because it is the slip multiplied by the synchronous speed, not the actual running speed. Option D is incorrect because it is the synchronous speed minus the slip, not the actual running speed.