Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another. Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth. Refraction is described by Snell's law, which states that the angle of incidence is related to the angle of refraction by $frac\{sin\; heta\_1\}\{sin\; heta\_2\}\; =\; frac\{v\_1\}\{v\_2\}\; =\; frac\{n\_2\}\{n\_1\}$ or $n\_1sin\; heta\_1\; =\; n\_2sin\; heta\_2$ where $v\_1$ and $v\_2$ are the wave velocities through the respective media.