Answer / thomas dsouza

The speed is given by the formula N=(120xf)/P where f is
the frequency say 50hz or 60hz and P is the no of poles.

A 4 pole motor shall be running at a speed of =(120x50)/4
that is 1500 rpm.

Answer / shahulsnfa

Mr. thomas you were saying about the rated speeed
(synchronous speed). the question is about the real speed
(shaft speed).

Answer / mr. kiru

shaft speed = synch speed-{(slip*synch speed)/100}

Answer / joshy govindan

IN COMMON MOTORS SLIP=4%
IN THAT CASE A MOTOR WITH SYNCHROUNOUS SPEED 1500RPM WOULD
BE A SHAFT SPEED = 1440 RPM
I think Mr. Kiru is correct

Answer / thomas dsouza

These questions are asked for interview purpose and one
likes to test the appplication of the academic knowledge of
the candidate at times in practical situations to know
about the particular equipment. This will not be accurate
for practical conditions. However, as you mentioned, the
speed mentioned was synchronous speed only and if one knows
the % slip it can be deducted to get the actual speed.

But for any purposeful recording/analysis of the actual
speed one may have to use a measuring instrument only to
get the exact values.

If there is a better answer anybody pls advice.

Answer / k.prakashchandra

Stroboscope,if the slip is not too much

a room heater is connected in serise with a 100w bulb.if the 100w bulb is replaced by a 40w bulb then the output of the heater is increase/decrease/remain same?

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