GCSE questions on refraction and TIR
Q3. Light usually changes direction as it passes from one medium into another. This occurs when the angle of incidence on the medium boundary is greater than 0o.
(a) Name the process that results in a change of direction when light passes from one medium to another.
Refraction 
(1 mark)
(i) When light passes from air into a glass block, it changes direction in such a way that it moves:
| away from the normal |
|
| towards the normal |
|
| to always travel along the normal |
|
(1 mark)
(ii) When light passes from glass out into the air, it changes direction in such a way that it moves:
away from the normal |
|
towards the normal |
|
to always travel along the normal |
|
(1 mark)
(b) Name the process that results in a ray of light 'rebounding' when it hits another medium.
Reflection
(1 mark)
(c) Name the process that occurs when a ray hits the boundary between a dense optical medium (such as glass) and a rare optical medium (such as air) at an angle of incidence that is greater than the 'critical angle'.
Total internal reflection
(1 mark)
(d) The diagram shows the path of a light ray through part of an optical fibre.
(i) Give one practical use for optical fibres.
Any one from:
within an endoscope for doctors to see inside a patients body or use in keyhole surgery
telephone cables (do not accept flex or wires for cable)
optical fibre or fibre optic lamps such as used in (artificial) Christmas trees and decorative/ ornamental lighting
data transfer or internet connection ( 'communications' did not warrent a mark unless clarified)
(1 mark)
(ii) Explain, as fully as you can, why the light ray stays inside the optical fibre.
Total internal reflection occurs making the ray reflect at the fibre boundaryrather than pass through it, this happens because when the ray hits the boundary between the fibre material and air the angle of incidence is greater than the critical angle for the material so no refraction occurs.
(2 marks)
(Total 8 marks)
About this site
In questions such as this your answer must clearly indicate how the otical fibre is used - just saying 'for doctors' or 'in lamps' will not get you any marks - be specific!
