Lenses [Physics only]

How lenses work

• A lens forms an image by refracting light
• In a convex (converging) lens, parallel rays of light are brought to a focus at the principal focus. The distance from the lens to the principal focus is the focal length
• A concave (diverging) lens spreads parallel rays out so they appear to come from the principal focus on the same side as the light comes from
• In ray diagrams a convex lens is drawn as a vertical line with outward-pointing arrows at each end; a concave lens as a vertical line with inward-pointing arrows