TOTAL INTERNAL REFLECTION Refraction Light moving from one

TOTAL INTERNAL REFLECTION

Refraction Light moving from one medium to another will bend towards or away from the normal, depending on the speed of light in the second medium.

Total Internal Reflection

Critical Angle The angle of incidence that produces an angle of refraction equal to Angle of 90 degrees. refraction Angle of incidence

Total internal reflection occurs when the incident ray is greater than the critical angle

Why do you see the reflection ?

Fibre Optic Cable

Critical Angle If the angle of refraction is 90 degrees then light will travel along the surface of the two mediums. Total internal reflection occurs when the angle of incidence is equal to or greater than the critical angle.

Total Internal Reflection If the angle of incidence exceeds the angle of refraction, the refracted ray will not exit the first medium. Rays reflect back into the same medium.

Total Internal Reflection 1. Light is traveling more slowly in the first medium than the second medium. Ø This means that the first medium has the largest index of refraction.

Total Internal Reflection The angle of incidence is large enough that no refraction occurs in the second medium. The ray gets reflected back into the first medium which occurs if the angle of incidence is equal to or greater than the critical angle.

Comparison of Angles of Refraction

Use of Internal Reflection Diamonds. ØDiamonds have the highest index of refraction, but can increase the amount of total internal reflection by being cut properly making diamond sparkle.

Use of Internal Reflection Fibre Optics. ØLight transmits information along a high purity glass or plastic cable.

Fibre Optics ØThe cable has a small critical angle. üBouncing light will always have an angle of incidence greater than the critical angle and thus stay within the cable.

Fibre Optics Uses üCommunications – phones, communications, TVs üMovie Industry üCar dashboard lights üMedical Industry – laparoscope surgery Endoscope

Glass Prisms ØCritical incidence of 41. 1°. ØReflect more than mirrors → mirrors absorb some light. ØSilver backing of mirrors deteriorates.

Glass Prism Design

Periscopes

Binoculars

Retro-reflectors Returns any light hitting it straight back towards the direction which it came from. Øthe corner of a glass cubes are used on many road signs to make them more noticeable.

Retro Reflectors A and B are corner cube reflectors. C is a corner cube retro-reflector after three corners have been ground down.

Other uses – bicycle reflectors.

Vocabulary Critical Angle Total Internal Reflection Fibre Retro-reflectors Homework Pg. 531 # 1 – 6, 8