Correct Answer - Option 2 : Six

**Concept:**

An induction motor works on the principle of electromagnetic induction. It is possible, only when there is a relative speed between the rotor, and synchronously rotating armature flux.

So, the rotor of an induction motor runs at a speed, less than its synchronous speed. The difference speed the rotor speed and the synchronous speed is called slip speed.

The synchronous speed of an induction motor is given by

\({N_s} = \frac{{120f}}{P}\)

Where f is the supply frequency

P is the number of poles

**Calculation:**

Given that, the speed of the induction motor (N_{r}) = 950 rpm

The synchronous speed (N_{s}) = 1000 rpm

Frequency (f) = 50 Hz

\({N_s} = \frac{{120 \times 50}}{P} = 1000\)

⇒ P = 6