The Critical Angle and Total Internal Reflection

Recall: Refraction Refraction: The bending of light as it passes from one medium into another.

Recall: Refraction

Recall: Snell’s Law

Dispersion Refraction of white light into seperate colours. Different colours travel at different speeds and have a different n value.

The Critical Angle (  c ) The angle of incidence where the light refracts along the boundary between the two mediums. sin  R = 90 o.

Total Internal Reflection Complete reflection of light back into the first medium. Light does not refract into the second medium.

Total Internal Reflection Two conditions must be met: – Light must be travelling from a more optically dense to a less optically dense medium. n1 > n2 – Angle of incidence (  i ) is greater than the critical angle (  c ).

Practice Problems What is the angle of refraction for light travelling from a diamond (n=2.42) to air (n=1.00) with an angle of incidence of 60°? n 1 = 2.42  1 = 60° n 2 = 1.00  2 = ? Sin  2 = n 1 sin  1  Sin  2 = 2.42sin60 n Sin  2 =   2 = sin -1 (2.096)  ERROR!

Practice Problems What is the critical angle for light travelling from a diamond (n=2.42) to air (n=1.00)? n 1 = 2.42  2 = 90° n 2 = 1.00  c = ?(in your equation, treat this as  1 ) Sin  c = n 2 sin  2  Sin  c = 1.00sin90 **sin90 = 1 n Sin  c = 1.00   c = sin -1 (0.413)   c = 24.4 ° 2.42

Refraction Applications Rainbows. Mirages. Binoculars. Fibre optic cables. Diamonds. Watch This!!!