Frequency

The frequency of an oscillatory phenomenon is the amount of oscillations it completes per unit time. For instance, in a simple pendulum, it can be interpreted as the number of swings it completes in a second or in a minute. It can be given in two different forms:

• the ordinary frequency is measured in $\text{cycles}/\text{s}$ or $\text{Hz}$ (or other unit of time) and is denoted $\nu$ or $f$;
• the angular frequency is measured in $\text{rad}/\text{s}$ (or other unit of time) and is denoted $\omega$.

The two are related by $\omega=\nu/2\pi$. A wave is said to be monochromatic if it composed of exactly one frequency. This curious term has traces its origin in the theory of electromagnetic waves, of which light is a kind. That theory teaches us that the color of light is determined entirely by its frequency, so a visible electromagnetic wave of singular frequency is perceived as precisely one color: monochromatic.