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

(angle of refraction > angle of incidence)

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°

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

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 1st medium than the 2nd

2. the angle of incidence is big enough that NO refraction occurs into the 2nd medium (only reflection back into the 1st medium)

* the larger the index of refraction, the smaller the critical angle *

Applications of Total Internal Reflection 1. Sparkling of Diamonds 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

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

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)

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

Ex. Binoculars, cameras, periscopes – see page 529

Examples…

Answer questions

Pg 531 # 1-5, 7, 8