Refraction Critical Angle Total Internal Reflection Total Internal

Refraction Critical Angle & Total Internal Reflection

Total Internal Reflection: p When light travels from one medium to another, refraction occurs, BUT also some reflection. p When light travels from a medium of higher to lower refractive index, light is reflected to a greater extent. p As angle of incidence increases, reflected ray gets stronger & refracted ray gets weaker.

Total Internal Reflection: p Until the angle of refraction reaches a maximum of 90 o (i. e. it’s along the surface of the medium) p At this point, refraction ceases & all light is reflected back Total Internal Reflection p The angle of incidence at which TIR occurs in the critical angle.

Refraction & reflection Air Glass R i r Air Glass Calculating the critical angle is easy since the angle of refraction is 90 o!!! R Refraction along medium surface & reflection i r Total internal reflection Air Glass i r

Calculate the critical angle for the interface between water (n=1. 33) & air (n=1) water air Recall: critical angle will only exist if going from high n to low n

Calculate the critical angle for the interface between crown glass (n=1. 52) & air (n=1) glass air

A jeweler wants to displace her diamonds in such a way that they capture the light & sparkle as much as possible. What is the incident angle that light must strike inside the diamond to ensure TIR? diamond air Recall:

Glass n=1. 5 Glass has a high critical angle (42 o), so light escapes Diamond n=2. 42 Light undergoes TIR before exiting Diamond n=2. 42 Diamond cutters Light exits b/c want TIR so must angle incidence cutthan at right less critical anglesangle plus want to allow light to exit the top

The angle of incidence of light in water & heading towards air in 50 o. Calculate the angle of refraction. water air The angle of incidence is greater than the critical angle, so TIR occurs, therefore no refraction

p Substances with higher indices of refraction refract the light to a greater degree & thus have lower critical angles

Applications: p Optical Instruments n Contain prisms that allow TIR Diamond cutters p Fiber Optics p Rain sensor wipers p Etc… p

Mark is lying by the side of a swimming pool and looking down at a light source located at the bottom of the pool, which is 1. 35 m deep. The refractive index of the water is 1. 33. If the light ray is to enter Mark's eye, at what maximum distance d from the side of the pool can the light source be located?

If further away, angle of incidence increases beyond critical angle & TIR occurs!

Use table on page 61