The degree of refraction depends on the angle of incidence as well as physical properties of the materials through which the light is propagating. The physical property of transparent materials related to refraction is called optical density, and the index of refraction is a measure of their optical density. Figure 1 Air is a transparent material. We ve already learned that light travels in a straight line through air. We can form a general rule that light will also propagate in straight lines in any transparent material.
Refraction occurs at surfaces or interfaces just as reflection does.
So, for these experiments we will illustrate light with straight lines inside a material and show bending or changes in direction of the lines only at surfaces or interfaces. Remember, the best way to describe a surface is by using the concept of a normal - a line perpendicular to the surface at the point of contact of the ray. In each case while studying refraction, think about whether the ray is bent toward or away from the normal. As a result of refraction, when we view an object through a transparent medium we do not see the object directly, we see an image of the object. In the following series of experiments we will measure the properties of images formed by refractive materials, the index of refraction of those materials, as well as investigate the dependence of refraction on the angle of incidence.