1. Light
Refraction of light including identification of the normal, angle of incidence and angle of refraction.
Description of refraction in terms of change of wave speed.

2. Refraction :
Waves change speed when they travel from on medium to another.
This means they sometimes change direction.

3. An analogy to explain refraction.
Soldiers marching on concrete and sand,
concrete
When they reach the sand the soldiers slow up.
The soldiers at the left of each row reach the sand first so slow before the ones at the right.
The column changes direction.
sand

4. Normal – at right angles to the boundary
air
i – incident angle
r – refracted angle
water r
Shine a single ray of light through a rectangular block. Draw where it goes on a diagram in your jotter.
You should draw an arrow each time the line changes direction.

5. Now use 3 rays of light to shine on the two lenses
Now use 3 rays of light to shine on the two lenses. The middle ray should go straight through.
Convex lens
Concave lens
Note the rays in and out of the rectangular block should be parallel.
All rays should have an arrow head on them each time they change direction.

6. When the angle in the air gets to 90o it can no longer be refracted and is then reflected. This is called total internal reflection.
Total internal reflection
refraction
Smaller than critical angle
Critical angle – when refracted angle is 90o
Larger than critical angle
demo

7. Use of total internal reflection - Optical fibre demo
Used as telephone ‘wires’ and in medicine in endoscopes etc

8. Endoscopes – to look inside people

9. Uses of refraction - Glasses
Hyperopia (farsightedness)
Normal eye
Myopia (nearsightedness)
Corrected with concave lens
Corrected with convex lens
No correction needed
Uses of refraction - Glasses
No one’s perfect
Demo of eyesight correction
Click on demo of eyesight correction to explain eye sight problems – or order lap tops and they can use the Boots Learning Store ( No one’s perfect) resource themselves.