Question

In an alternator, frequency per revolution is equal to ___________

(a) number of poles

(b) twice the number of poles

(c) speed in rps

(d) number of pole-pairs

I got this question in an interview for job.

This question is from Generated EMF in chapter Principles of Electro mechanical Energy Conversions of Electrical Machines

Answer 1

The correct choice is (d) number of pole-pairs

Explanation: For a P-pole machine, in n rev/sec, P/2n cycles/second are generated and cycles per second is referred to as frequency f of the EMF wave. Here in this question n=1

⇒ frequency per revolution = P/2

⇒ number of pole pairs.