WAVES 4 : Total Internal Reflection

1
WAVES 4 Total Internal Reflection

• By the end of this presentation, you should be
  able to
• Recognise diagrams showing TIR
• Recall what conditions must be met in order for
  TIR to occur.
• Draw diagrams to illustrate TIR of light in
  glass.
• Describe applications of TIR.

2
Total Internal Reflection

• Occurs only if the light is passing into a less
  dense material. So it cannot happen if the ray is
  travelling from air into glass (or water).
• Happens only at certain angles ( when the light
  hits the glass (or water) surface at an angle of
  incidence that is greater than the critical angle.

3
Total internal reflection of light in water
When the ray hits at 90o, it passes straight out
into the air.
As the angle of incidence (in water) is
increased, refraction is observable.
If the angle of incidence (in water) is too
large, refraction will not be allowed and the
wave is reflected internally.
4
TOTAL INTERNAL REFLECTION

• Look carefully at the following slides. It shows
  the stages leading up to total internal
  refraction.

5
TIR only takes place when light travels into a
less dense material, eg, from glass into air
This angle of incidence is very small.
The ray is refracted as usual
r
normal
i
6
As you increase the angle of incidence in glass,
the angle of refraction in the air will increase
too.
7
When the angle of incidence has increased so much
that the angle of refraction is 90o, you have
reached a special angle.
r 90
When the angle of
refraction is 90o, the special
angle of incidence is called the critical angle.
8
If the angle of incidence is increased any more,
so that it is larger than the critical angle,
total internal reflection occurs.
9
Uses.

• Information is sent along optic
• fibres in communication
• systems. It has the advantage
• of being more secure than
• copper wires, and more
• information can be sent along
• one cable.
• Optic fibres can be used in
• medicine as well. Endoscopes
• can be inserted into small
• incisions, or can be pushed
• down the throat so the inside
• of the body can be seen without
• surgery.