Light — Reflection and Refraction — Revision Notes

In reflection the angle of incidence equals the angle of reflection, and the incident ray, reflected ray and normal all lie in the same plane. A concave mirror can form real or virtual images depending on where the object is placed, while a convex mirror always forms a small, virtual, erect image — which is why it is used as a rear-view mirror. Refraction is the bending of light when it passes from one medium into another because its speed changes; the amount of bending is given by the refractive index. A convex lens converges light and a concave lens diverges it. The mirror and lens formulas relate object distance, image distance and focal length, and the power of a lens is the reciprocal of its focal length in metres.