You Are Going to Find out How Light Changes Direction As a Ray Passes Through a Block of Glass

You are going to find out how light changes direction as a ray passes through a block of glass.

Apparatus

glass or plastic blocks (various shapes) / plain paper
raybox / power supply
single slit

Health and safety

• Rayboxes often get very hot, so take care not to get burnt.

• If you use glass blocks, take care not to drop or damage them.
Take special care if the blocks are already damaged.

Method

A Place a piece of plain paper on the desk. Set up the power supply, raybox and single slit so that you can shine a single ray of light across the paper on your desk.

B Place a block on the paper. Shine the ray into your block to observe how its direction changes at each interface. You can see the path of the ray by looking down into the block.

C Change the angle at which your ray hits the interface and observe any difference from the first setup.

D Repeat with the ray coming in at various different angles.

Prediction

1 Before you start, draw round the block on a piece of paper and draw in the direction of a ray you intend to send into it. Then add a ‘prediction’ ray to show what direction you think the light will travel as it passes through.

Recording your results

2 Draw diagrams of the results. Add normal lines to your diagrams and label the incident and refracted rays.

Considering your results/conclusions

3 a What did this experiment show you about how light changes direction on entering and leaving a glass block?

b How are entering and leaving different?

Evaluation

4 The instructions on this sheet are for a general investigation to produce a qualitative result. How could you make changes your experiment so that it could show you a relationship between the angle at which the light ray hits the interface and its direction inside the glass block?

This document may have been altered from the original.

1 The drawings show two diagrams of a mug. Highlight the rays of light that show why you can see the coin when there is water in the mug but not when it is empty.

2 A pencil standing in a beaker of water appears to bend where it enters the water. Complete the rays of light in this diagram to show why this happens.

3 If you look at writing through a block of glass, the words appear to be closer than they really are. Complete the rays of light in this diagram to show why this happens.

4 Coins in the bottom of a wishing well look close enough to pick up, but when you try you cannot reach them. Add rays of light to this diagram to explain why the coins appear closer than they really are.

This document may have been altered from the original.

1 Add labels to this diagram using the words and phrases in the box. You may need to use some of the words more than once.

angle of incidence / angle of refraction / incident ray / normal / refracted ray

2 Continue drawing the ray of light to show what happens when the light goes into the glass.

3 The diagram shows a ray of red light passing through two prisms.

a What do the dashed lines represent?

b Show what happens to a ray of violet light passing through the two prisms.

Hint: Violet light bends (changes direction) more than red light when it refracts.

4 Imagine you have found an old pair of glasses with converging lenses. Draw a diagram to show how you would find the focal length of the lenses.

This document may have been altered from the original.

1 Continue the ray in each of the diagrams to show what happens when the ray of light reaches the boundary.

2 Imagine you have found an old pair of glasses with converging lenses. Draw a diagram to show how you would find the focal length of the lenses.

H 3 The table shows how fast light travels in different materials.

Material / Speed of light (m/s)
air / 300 000 000
glass / 200 000 000
water / 225 000 000

a What happens to the speed of light when it travels from air into water?

b Will light be refracted more when it goes from air to glass or from air to water?
Explain your answer.

H 4 The diagram shows a ray of red light passing through two prisms.

Copy the diagram.

a What do the dashed lines represent? ______

b Mark with an X two places where light is slowing down.

c Mark with a Y two places where light is speeding up.

d Show what happens to a ray of violet light passing through the two prisms.

Hint: violet light is refracted through a bigger angle than red light when it enters a prism.

H 5 The diagram shows a ray of light going through a glass block. Use the information on the diagram to help you to fill in the gaps in the paragraph below.

When light travels from air into ______the wave speed ______. The light ray bends ______the normal. When the light re-enters the air its speed ______and it bends ______from the normal. This is an example of ______occurring.

This document may have been altered from the original.