Explain refraction through a parallel-sided glass slab.

• Refraction is the change in the direction of a wave passing from one medium to another.
• A light ray refracts whenever it travels at an angle into a medium of a different refractive index. This change in speed results in a change in direction.
• In this instance, we move the glass slab around the air or another rarer substance.
• The light rays would now go in the direction of normal if the medium were denser.
• Snell's law may now be used to determine how much these rays are deflected as a result of refraction.
• According to Snell's law, "for the light of a given color and for the given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant."