Snell’s Law explains the focusing of light by curved lenses by describing how light bends when it enters and exits the lens surfaces, which have different curvatures and materials with different refractive indices compared to air.
- Refraction at curved surfaces:
A curved lens has two surfaces—usually convex or concave. When light passes from air into the lens material (like glass or plastic), it bends because the refractive index of the lens is higher than that of air. Snell’s Law governs this bending, which depends on the angle at which light strikes the curved surface and the difference in refractive indices. - Converging or diverging effect:
In a convex (converging) lens, light rays that enter parallel to the principal axis bend inward toward a focal point after refraction. In a concave (diverging) lens, they bend outward as if they came from a virtual focal point. This change in direction happens twice—once when entering the lens and again when exiting—each time governed by Snell’s Law. - Focus formation:
The curved shape ensures that rays entering at different points are bent at different angles. Snell’s Law explains this variable bending, which causes the rays to either come together at a point (focus) or spread apart.
Thus, the lens shape and refractive index, through Snell’s Law, determine how light rays bend and focus.