The frequency of a wave can be described using two definitions:

  1. Frequency, f, is proportional to the reciprocal of the wavelength, λ, and is related to the speed of light(c) in a vacuum. This means that longer wavelengths correspond to lower frequency and shorter wavelengths correspond to a higher frequency, according to the following equation:

  2. Frequency is also defined as the number of complete cycles occurring per period, T, of time. The SI unit of frequency is Hertz, defined as 1 Hz = 1 s-1. The shorter the period, the larger the frequency.

The following equation defines frequency as the reciprocal of the period of the oscillation, T: