What is the frequency of a alternator, if ___

What is the frequency of a alternator, if P = number of poles and N = revolution made per second?

A. PN / 2 Hz.
B. 120 / PN Hz.
C. 120N / P Hz.
D. 120P / N Hz.

Show Answer

Answer: A

Share your understanding of this question with the correct explanation.

The answer is A. PN / 2 Hz.

The frequency of an alternator is the number of cycles of AC produced per second. The frequency is determined by the number of poles and the speed of rotation.

The formula for calculating the frequency of an alternator is:

Frequency = PN / 120`


  • P = Number of poles
  • N = Speed of rotation in revolutions per second
  • 120 = Constant

For example, an alternator with 4 poles rotating at 1000 revolutions per minute (rpm) will have a frequency of:

Frequency = 4 * 1000 / 120 = 33.33 Hz