# When a 400 V 50 Hz 6 pole induction motor is running at 960 rpm on no load, its slip is

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When a 400 V 50 Hz 6 pole induction motor is running at 960 rpm on no load, its slip is
1. 1%
2. 4%
3. 3%
4. 2%

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Correct Answer - Option 2 : 4%

Concept:

In a 3-phase induction motor, the synchronous speed can be calculated as

${N_s} = \;\frac{{120f}}{P}$

$s = \;\frac{{{N_s} - {N_r}}}{{{N_s}}}$

Where, Ns = Synchronous speed in rpm,

N= Rotor speed in rpm,

s = Slip of the machine,

f = Supply frequency in Hz,

P = Number of poles,

Calculation:

${N_s} = \frac{{120 \times 50}}{6} = 1000\;rpm$

$s = \frac{{1000 - 960}}{{1000}} = 0.04$