## Snell's Law, Frequency, Speed and Wavelength

When a wave is refracted at the boundary it is not only the direction of the wave that changes. The speed and the wavelength also change. For light, we can use Snell's Law:
$n= \frac{sin \theta_1}{\sin \theta_2}$
.

In fact
$n=\frac{v_1}{v_2}= \frac{\lambda_1}{\lambda_2}$
.
These relationships mean that as waves pass from medium to medium, the sin of the angle between the wave and the normal, the speed and the wavelength all change in proportion. The frequency is not changed.
Not all wave behave in the same way on passing from air to gall or water. Light slows down, nut sound speeds up dramatically. The speed of sound in air is about 330m/s, but the speed of sound in water is about 1500m/s.