Define refraction.

• A. The reflection of light from a surface.
• B. The bending of light as it changes medium, due to a change in speed.
• C. The absorption of light by a material.
• D. The production of light by a source.

Answer: (B)

Refraction is the bending of light as it passes from one medium into another because its speed changes. When light crosses a boundary into a material where it travels slower or faster, its path pivots at the boundary. The amount of bending depends on the angle of incidence and the optical densities (refractive indices) of the two media. If light slows down entering a denser medium, it bends toward the normal; if it speeds up entering a less dense medium, it bends away from the normal. This effect is described by Snell’s law. A familiar example is a straw in a glass of water appearing to bend at the water’s surface. The other statements describe different phenomena: light reflected off a surface, light absorbed by a material, and light produced by a source.