Refraction

Refraction The bending or change in direction of light when it travels from one medium into another.

Index of Refraction

When light moves from a faster medium to a slower medium, it bends ….. Speed of light (m/s) n ∠i 1.00 3.00 x 108 vacuum 1.33 2.26 x 108 water ∠R

When light moves from a slower medium to a faster medium, it bends ….. when n2 is less than n1 ∠R n2 = 1.00 air n1 = 1.33 water ∠i ∠i is less than ∠R

air water ∠ican be any angle What happens when you keep increasing the angle of incidence?

∠R air water ∠i If ∠R becomes 90° ∠i must be less than 90° Critical angle

Critical Angle the angle of incidence that produces a refracted angle of 90°. Only occurs when n1 is greater than n2 A physical property of the medium.

What happens when an incident angle is greater than the critical angle? ∠R air water ∠i Reflection occurs on the surface. critical angle Critical angle for water: 48.8° Total Internal Reflection

Total Internal Reflection When the angle of incidence is greater than the critical angle, light is reflected at the surface of the medium. Note: only occurs when n1 is greater than n2

critical angle for diamond: 24.4° Refraction in a diamond

Refraction in a diamond

Fibre Optics

www.youtube.com/watch?v=0MwMkBET_5I Fibre Optic Cables

The speed of communications

Fibre Optics – endoscope

45° 45° Triangular Prism

45° 45° 45° 45° Triangular Prism

Triangular Prism

Plane Mirrors vs. Triangular Prisms: • In triangular prisms almost 100% of light is reflected. Mirrors absorb some light, reducing quality. • More durable. Opaque surfaces in mirrors often deteriorate over time. Triangular Prism

Retro-reflectors and Prisms

Retro-reflectors and Prisms An optical device in which the emergent ray is parallel to the incident ray

Diagram of a Retro-reflector

Retro-reflectors – examples

Refraction

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