NOTE:  This page assumes the reader has some familiarity with waves and the different representations of waves.  If you are unfamiliar with terms such as wavefront or plane wave, see this page of the Introduction to Waves module. Two other good reviews of wave properties can be found at this site from the University of the Pacific and this site from Mainland High School.

Refraction refers to the bending of light.  The animation below illustrates why a beam of light will bend.  Click on the number of the next frame to continue through the animation.  Click replay to see the same frame again.

This animation illustrates several important points.  One such point is that the wavefronts get closer together as the light enters the denser material.  Indeed, the wavelength of light is determined in the same manner as the speed: by the index of refraction.  The wavelength of light λ_n in a given medium having index of refraction n is found by

where λ₀ is the wavelength of light in vacuum.  The frequency of light is unchanged as the light moves from one medium to the other.  Click here for an explanation.

The animation also illustrates that refraction occurs because a wavefront moving from air to water at an angle to the water's surface does not reach the water all at once.  Initially, just one side of a wavefront reaches the water and slows down. Just as a row of soldiers marching in formation goes around a corner when the members at one end of the row walk slower than the members at the other end of the row, a wavefront encountering the water bends as one end enters a denser medium.  As was explained on the page about reflection, angles are always measured with respect to the normal to the interface between two media.  The relationship describing how light refracts is called Snell's Law and is the topic of the next page.
 

How can we determine how far the light will bend? Continue to the next page to find out!