Transcript Total Internal Reflection and Medicine

Total Internal Reflection and
Medicine
What is TIR and how is it used in the
medical profession?
Starter: how can doctors see inside
people? List as many ways as
possible.
Glossary
• Total Internal Reflection –
• http://www.bbc.co.uk/learningzone/clips/tota
l-internal-reflection/13524.html
•
Demo
• Watch the demo. Look out for the critical
angle.
This is TIR. The
angle of
incidence is
greater than
the critical
angle.
The angle of
reflection
equals the
angle of
incidence.
Here there is
partial
reflection and
some
refraction.
The angle of
incidence here
is called the
critical angle.
This is reached
as the
refracted line
emerges on
the boundary.
HIGHER only (F – read over notes and
complete any questions)
• To Calculate the critical angle…..
Sin c = 1/n
Where c is the angle of incidence.
n = refractive index
e.g. Calculate the critical angle for glass with a refractive index of 1.59.
Sin C = 1/1.59
Sin C= 0.629
C = 39 degrees.
Using TIR
Optical fibres – these transmit light or IR
radiation.
Light travels down the fibres and cannot escape
because it is TIR each time it bounces off the
fibre.
Endoscope
http://www.bbc.co.uk/l
earningzone/clips/medic
al-uses-of-visible-lightthe-electromagneticspectrum/1456.html
• Used to see inside people without surgery.
• There are 2 fibres.
– 1 shines light
– 1 has a lens and forms images on the fibre ends.
• Laser light – can be used to burn away
diseased tissue, close up blood vessels.
e.g. laser eye surgery !
Task
• Read page 214- 215
• Draw figure 1 and describe how TIR and
optical fibres work.