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

Ask pupils to estimate their top speeds on land and in water.
- Land: 10m/s (100m runner); water: 2.4m/s (50m swimmer) use this to link to the idea that the speed of light changes depending on the material it's travelling through.

If you have time to spare the following is a nice way into looking at the sine function:
- 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.
Prior to starting the experiment it may be worth ensuring that pupils can use the sine function on their calculator and that they are working in degrees.
Run through the refraction experiment and have pupils draw a table with 5 columns. Once they have 4-5 readings for i and r they need work out sin i and sin r. Finally the last column should be n. If you have time they can plot sin i against sin r to get a better value of n.It may be useful to leave on the board a diagram showing which angles to measure. Also reiterate that they should be measuring between the ray and the normal line and not the surface. Some pupils will struggle collecting the data, so have some spare on hand for them so they can still carry out calcuations and plot the graph.
Once they have Snell's law have them carryout some calculations and go through how to make i and r the subject of the equation.

Rayboxes get hot avoid touching. When operating in limited light walkways need to be kept clear and pupils should take care when moving around.