# What is the formula for frequency?

Frequency, $f$, is the number of oscillations in the unit of time (1 second) and is given as the reciprocal of the Period, $T$, (which is the time taken for one complete oscillation) so:
$f = \frac{1}{T}$ measured in ${s}^{-} 1$ called Hertz.
Frequency is also related to wavelength, $\lambda$, as: $c = \lambda \cdot f$ where $c$ is the speed of light.
Also, frequency is related to Energy, $E$ (of a photon), through the Einstein's relationship: $E = h \cdot f$ where $h$ is Planck's Constant.