Rays and Reflection A large number of electromagnetic waves all moving in the same direction at the same time constitute what is called a wave front . Since each wave within it consists of a small bundle of wavelets that were emitted together as a pulse, it is common to speak of these waves as if they were particles called photons . (In truth, a photon has properties of both a particle and a wave.) A ray is a series of wave fronts and is directed perpendicular to those fronts. It is important to understand that it is possible for a ray of light and the photons that compose it to be moving in slightly different directions. A wave front acts as if it is constantly rebuilding itself out of a huge number of spherically emitted waves from each point on its surface. The sideways components of these spheres cancel out and only the advancing front remains. This may seem like an unnecessary complication, but it explains some of the more peculiar behaviors of light rays that we will discuss later.
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