Physics Classroom
The Physics Classroom: Refraction and Ray Model of Light: The Critical Angle
Illustrated examples and interactive practice problems that introduce students to the concept of the critical angle, the angle of incidence that provides an angle of refraction of 90-degrees.
Boston University
Bu: Optics: Geometric Optics
Several short descriptions of demonstrations which illustrate principles of geometric optics (many of which focus upon refraction).
BBC
Bbc: Gcse Bitesize: Why Do Scientists Think That Light and Sound Are Waves?
Light travels as transverse waves and can travel through a vacuum. Sound travels as longitudinal waves and needs to travel through a solid, liquid or gas. Read about the properties of light and of sound, and learn the differences between...