Post on 11-Dec-2015
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