Concept preview

What you will be able to do

1. 01Distinguish converging and diverging lenses and their focal points
2. 02Use the thin-lens equation and magnification
3. 03Explain how the eye focuses and how glasses correct vision

A lens bends light by refraction at its two curved surfaces. A converging (convex) lens is fat in the middle and, as its name says, brings parallel rays together to a point. A diverging (concave) lens is thin in the middle and spreads parallel rays apart. Cameras, projectors, magnifiers, and your own eye all rely on converging lenses; diverging lenses fix short sight and form peepholes.