The ray model of light states that light is a particle and not a wave. Imagine a ball bouncing (reflecting) off a wall, light behaves in the same way. In this model, light is represented by a ray (or line). For the study of optics, treating light as a particle is very useful. However, you have just learned that light is also a wave.

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Ray Model

Scienctists argued for years over which model was to be used to describe light. They finally agreed that to fully describe all the properties of light that both models were necessary. This has now become to be known as the wave-particle duality model. So light behaves as a wave or a particle, but not both at the same time.

Light & Matter

When light strikes a material three things can happen:

• light may be absorbed
• light may be reflected
• light may be transmitted (pass through it)

 

Opaque Materials: prevent any light from passing through it. Most solid objects are opaque.

Translucent Materials: some light is transmitted or scattered different directions. Frosted glass or a lampshade are examples of translucent materials. Objects can not be seen clearly through translucent materials.

Transparent Materials: allow most or all of the light to pass through it. Objects can be clearly seen through transparent materials.

Shadows: opaque objects create shadows. You can use the ray model of light to predict where shadows will form and how large they will be. To do this we draw rays of light from the source that just pass by the edge of the opaque object. Where there are no light rays, a shadow will be created.

You may have noticed that some shadows are not perfect, there is some fuzziness near the edges. This is because some light is blocked while some light is entering the shadow. The darkest area of a shadow is the umbra, while the partial shadow is the penumbra. The best examples of these occur during eclipses.