Reflection and RefractionReflection and Refraction

ReflectionReflectionTwo laws of reflectionAngle of incidence = angle of reflectionThe angle of incidence, angle of reflection

and normal all lie in the same plane

RefractionRefraction

Light travels more slowly in glass, perspex etc than in air or in a vacuum

If light meets a block of glass etc head on it goes straight through

If light meets a block of glass etc at an angle it bends

Refractive IndexRefractive Index Light travels fastest through a vacuum Light travels more slowly through other materials like glass, water or

perspex The Refractive Index links the speed of light in a vacuum to the speed of

light in a medium

Refractive index n = speed of light in a vacuum speed of light in the medium

n = 1.33 for water n = 1.5 for glass (approx – depends on the glass)

Laws of RefractionLaws of Refraction Law 1 Snell’s Law

Law 2 The incident ray, refracted ray and normal all lie on the same plane

n = sin i

sin r

Relative Refractive IndexRelative Refractive Index

When a ray travels from one medium to another, the relative refractive index is

n(first medium)n(second medium)

and you use this relative n in Snell’s Law

Calculations using the laws of Calculations using the laws of refractionrefraction

1. Calculate the relative refractive index

2. Relative n = n (for first medium) n (for second medium)

3. Use the relative n in Snell’s Law to solve the problem