As a light wave moves from one medium into another, its speed changes

If the wave enters the new medium at an angle, the wave will change direction

Refraction

the change in direction of a wave as it changes speed while moving from one medium to another

Other examples of refraction

prisms

Diamonds

Rainbow

Refraction and lenses

​A lens is a transparent object with at least one curved side that causes light to change direction.

Convex Lens: Light rays that move through a convex lens come together or converge. Convex lenses are also called converging lenses.

​Convex lens images

Concave Lens: as light rays move through a concave lens, they spread apart, or diverge. Concave lenses are often called diverging lenses.

​Concave lens images