Refraction Through Uniform and Variable Thickness Glasses

(a) Refraction is the change in direction of a light ray when it passes into or out of a transparent medium
such as glass. A light ray that enters a denser medium, like going from air into water or glass, is bent or refracted to an
angle more perpendicular to the surface than the angle at which it was originally traveling. If the glass is flat, then the
light leaving it is refracted back to the direction it had before entering the glass. There is no overall change in the direction
in which the light travels. (b) If the glass is in the shape of a suitable convex lens, parallel light rays converge to a focus at
the focal point. As with parabolic mirrors, the distance from the lens to the focal point is called the focal length of the lens.