If AC power cycles back and forth 50 times per second, what is its frequency?

The frequency of an AC power source is defined as the number of cycles it completes in one second, measured in Hertz (Hz). In this scenario, if AC power cycles back and forth 50 times per second, the frequency is simply 50 cycles per second. Therefore, the correct answer is 50 Hz, which aligns with the standard measure of frequency in electrical systems.

When evaluating the other options presented, 30 Hz, 40 Hz, and 60 Hz all represent different frequencies that would indicate the AC power is cycling fewer or more times than stated in the question. Since the question specifically mentions that the AC power cycles back and forth 50 times per second, these alternatives do not accurately reflect the information given. Thus, understanding that frequency directly corresponds to the number of cycles per second clarifies why 50 Hz is the correct answer.