Outcomes

Pupils understand that light travels at different speeds in different media.
Pupils understand that the changing speed of light leads to the pheonmenon of refraction.

Specification References

3.14 recall that light waves are transverse waves which can be reflected, refracted and diffracted
- Diffraction is SA only
3.17 describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms
3.18 recall and use the relationship between refractive index, angle of incidence and angle of refraction
3.19 describe an experiment to determine the refractive index of glass, using a glass block
3.21 recall the meaning of critical angle c

Ask pupils to estimate their top speeds on land and in water.
- Land: 10m/s (100m runner); water: 2.4m/s (50m swimmer)

Show pupils the Trigonometry Triangle
Have pupils plot a sine curve on graph paper, from 0 to 360 degrees every 30 degrees. (Use scale 2cm = 30 degrees.)
Talk about the relationship between angle and sine(angle) and about inverse sine by "reading across" from the graph and down to angles. Smarter pupils might note that values "repeat" - that there are two possible angles that give the same sine value - this can be dismissed by pointing out that an angle of more than 90° is less than 90° in the other direction.