What happens when light enters a transparent medium (e.g. water)? What is refraction? What happens when light enters a transparent medium (e.g. water)? The light is partly reflected and partly transmitted.

The light bends when it crosses the air-water boundary – refraction Imagine that you are fishing at sunset… The light is partly reflected The light is partly transmitted The light bends when it crosses the air-water boundary – refraction

The bending of light when it travels from one medium to another is called refraction of light. Light travelling from air to glass at an angle normal incident ray The light ray bends towards the normal. angle of incidence air glass angle of refraction refracted ray

Light travelling from air to glass parallel to the normal Light travelling from glass to air at an angle normal incident ray angle of incidence glass air air glass angle of refraction refracted ray The light ray bends away from the normal. The light ray does not bend.

Laws of refraction Graph of sin i against sin r normal 0 90 A straight line through the origin sin r

The refraction of light across the boundary between two media obeys the laws of refraction. 1. The incident ray, the normal and the refracted ray all lie in the same plane. 2. Snell’s law: Simulation: Laws of refraction

Refractive index Consider a light ray travelling from air to a medium X, From Snell’s law, normal a air medium X X nX – refractive index of medium X

What is the physical meaning of the refractive index of a material? The degree of refraction of light as it travels from air into that material. The larger the refractive index, the more it bends the light.

Refractive indices of some common materials Refractive index air at 20C 1.00 water 1.33 perspex 1.50 glass (crown) 1.52 diamond 2.42

Light travels slower in an optically denser medium. A material with a comparatively larger refractive index – optically denser e.g. Diamond (nd = 2.42) is optically denser than water (nw = 1.33). Water (nw = 1.33) is optically denser than air (na = 1.00). Light travels slower in an optically denser medium.

When a light ray enters a material with larger refractive index, When a light ray entering a material with smaller refractive index, normal normal the light ray bends towards the normal. the light ray bends away from the normal.

That’s the end of Section 14.1 Check Point Key Ideas Previous Page Section 14.2 Exit