Total Internal Reflection and Medicine What is TIR

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.