If the synchronous speed of a 12 pole,...

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Question 1 of 205eccefa4bacbc34ba4d481eb

If the synchronous speed of a 12 pole, polyphase, induction motor operating at 60 Hz were 600 RPM, how many poles will be required in a similar motor operating at the same frequency but having a synchronous speed of 900 RPM?

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🔍 Key Concepts

• Synchronous speed formula for AC induction motors (relationship between frequency, poles, and RPM) • How changing the number of poles affects synchronous speed when frequency is constant • Comparing the original motor (12 poles, 600 RPM) to the new motor (unknown poles, 900 RPM) at the same frequency (60 Hz)

💭 Think About

• Write down the general formula that links synchronous speed (Ns), frequency (f), and number of poles (P), then solve it for P. • Check what happens to synchronous speed when you increase or decrease the number of poles, assuming frequency stays at 60 Hz. • Use the known case (12 poles, 600 RPM) to confirm your formula is correct before applying it to the 900 RPM case.

✅ Before You Answer

• Be sure you are using synchronous speed in RPM, not slip speed or rotor speed. • Confirm that frequency stays the same (60 Hz) in both problems, so only the number of poles is changing. • After calculating the required poles, verify it matches one of the multiple‑choice options and that the change in poles makes sense with the change in speed (fewer poles → higher speed, more poles → lower speed).

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