* Relationship: Frequency and period are inversely proportional. This means:

* As the period (time for one complete wave cycle) increases, the frequency (number of cycles per second) decreases.

* As the period decreases, the frequency increases.

* Formula:

Frequency (f) = 1 / Period (T)

* Calculation:

f = 1 / 0.2 seconds

f = 5 Hz (Hertz)

Therefore, the frequency of the wave is 5 Hz.