Question

A water wave rises and falls twice every four seconds. What is the period of the wave? What is its frequency?

Answer 1

Period = 2 seconds.
frequency = 1/2 cycle/second = 1/2 Hz

If it falls twice every four seconds, then it falls once every two seconds, therefore one falling period is two seconds.

Hz is equal to cycles per second. So if it goes through one cycle per two seconds, then it goes through 1/2 cycle per one second.

Hope this helps!