Obtain relationship between the time period and frequency.

If T is the time period of a wave, then by definition

In time T, the number of waves = 1

∴ In 1 second, number of waves (or frequency) =

$f = \dfrac{\text{1}}{\text{T}}$

Thus,

$\text{frequency} = \dfrac{\text{1}}{\text{Time period}}$

or

$\text{time period} = \dfrac{\text{1}}{\text{frequency}}$