Total Internal Reflection

Remember – when light goes from a more dense medium to a less dense medium it speeds up & bends away from the normal Remember – when light goes from a more dense medium to a less dense medium it speeds up & bends away from the normal (angle of refraction > angle of incidence) (angle of refraction > angle of incidence) As the angle of incidence, the angle of refraction until reaching the critical angle As the angle of incidence, the angle of refraction until reaching the critical angle Critical angle – the angle of incidence that results in an angle of refraction of 90° Critical angle – the angle of incidence that results in an angle of refraction of 90°

Total Internal Reflection If the angle of incidence is past the critical angle, there will be no refraction of the light, it will only reflect back into the medium If the angle of incidence is past the critical angle, there will be no refraction of the light, it will only reflect back into the medium Total internal reflection – when the angle of incidence is greater than the critical angle Total internal reflection – when the angle of incidence is greater than the critical angle

Total Internal Reflection occurs when 1. Light is travelling more slowly in the 1 st medium than the 2 nd 1. Light is travelling more slowly in the 1 st medium than the 2 nd 2. the angle of incidence is big enough that NO refraction occurs into the 2 nd medium (only reflection back into the 1 st medium) 2. the angle of incidence is big enough that NO refraction occurs into the 2 nd medium (only reflection back into the 1 st medium) * the larger the index of refraction, the smaller the critical angle * * the larger the index of refraction, the smaller the critical angle *

Applications of Total Internal Reflection 1. Sparkling of Diamonds 1. Sparkling of Diamonds n = 2.42 for diamonds and the critical angle is 24.4° most incident light undergoes total internal reflection n = 2.42 for diamonds and the critical angle is 24.4° most incident light undergoes total internal reflection Light rays bounce around many times inside the diamond before exiting out the top Light rays bounce around many times inside the diamond before exiting out the top The ideal cut of a diamond leads to the most total internal reflection The ideal cut of a diamond leads to the most total internal reflection

2. Fibre Optics Uses light to transmit information along a glass cable Uses light to transmit information along a glass cable Cable has a low critical angle so that light does not escape but continues to reflect inside the cable Cable has a low critical angle so that light does not escape but continues to reflect inside the cable Used in phone lines, computer cables, TV cables, medical devices (endoscopes) Used in phone lines, computer cables, TV cables, medical devices (endoscopes)

Examples of fibre optics

3. Triangular Prisms Many optical devices use prisms instead of mirrors to reflect light because mirrors absorb some light and mirror surfaces break down over time Many optical devices use prisms instead of mirrors to reflect light because mirrors absorb some light and mirror surfaces break down over time Ex. Binoculars, cameras, periscopes – see page 529 Ex. Binoculars, cameras, periscopes – see page 529

Examples…

Answer questions Pg 531 # 1-5, 7, 8 Pg 531 # 1-5, 7, 8