This page is a continuation of a tutorial about light reflection and refraction. It contains a diagram and suggestions on how to derive Snell's Law, which governs the refraction of light in a medium. For background to this derivation, first look at the page "How does light travel?," (link is at the bottom of this page) which introduces Fermat's principle and gives suggestions on how to derive the law of reflection. Beyond the derivation of Snell's Law, this page also contains investigation questions that will allow you to further explore the refraction of light.