# An Induction Motor is expected to run at 950 rpm at full load. With a power supply of 50 Hz. What could be the number of poles in the IM?

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An Induction Motor is expected to run at 950 rpm at full load. With a power supply of 50 Hz. What could be the number of poles in the IM?
1. four
2. Six
3. Eight
4. Two

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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 (Nr) = 950 rpm

The synchronous speed (Ns) = 1000 rpm

Frequency (f) = 50 Hz

${N_s} = \frac{{120 \times 50}}{P} = 1000$

⇒ P = 6