Wave equation

A pulse traveling through a string with fixed endpoints as modeled by the wave equation

Spherical waves coming from a point source

A solution to the 2D wave equation

The wave equation is a second-order linear partial differential equation for the description of waves or standing wave fields such as mechanical waves (e.g. water waves, sound waves and seismic waves) or electromagnetic waves (including light waves). It arises in fields like acoustics, electromagnetism, and fluid dynamics.

This article focus on two-way waves in classical physics. Single mechanical or electromagnetic waves propagating in a pre-defined direction can also be described with the first-order one-way wave equation, which is much easier to solve and also valid for inhomogeneous media. Quantum physics uses an operator-based wave equation often as a relativistic wave equation.