Students model how sunlight spreads across the ground using a torch and tilting board.

Apparatus and Materials

Each pair of students will need:

• Mini-whiteboard or board with paper attached
• Torch or lamp
• Cardboard cylinder
• Two different coloured marker pens
• Protractor (optional)

Procedure

Ask the students to:

1. Put a cardboard cylinder around the end of the lamp/torch.
2. Place the board so that it is perpendicular to the light source.
3. Use a marker pen to draw around the area where the light falls.
4. Place the board at an angle and use a different coloured marker to draw around the new area where the light falls.

Discussion prompts

• Which angle results in the light spreading out least?
• Which part of the world could this represent?

Teaching Notes

The light spreads out least when it strikes the board perpendicularly. Some students may think that this corresponds to summer in the UK. Explain why the curvature of the Earth’s surface means that this is not possible. The sun's radiation can only strike the ground perpendicularly in countries near the equator.

To model midday on the first day of summer they should tilt their board to 58°. For the first day of winter in the UK its 12°. It is warmer in summer because the sun's radiation is spread out over a smaller area and so the ground warms up more quickly.

Learning outcome

Students explain why the angle with which the sunlight strikes the ground changes over the year and how this contributes to it being warmer in summer.

This experiment was safety-tested in March 2020.