Objects of the same shape and size can make shadows that differ in darkness. A material that blocks more light leaves less light reaching the corresponding part of the screen. A material that lets some light through can leave a lighter patch.
The MOE Primary Science syllabus covers shadow formation when light is completely or partially blocked. This example keeps the shape and distances fixed and changes the material.
- Keep the light source and screen in the same positions.
- Use pieces of the same size and shape.
- Change the material between trials.
- Compare how bright the corresponding patch looks.
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Keep the outlines comparable
Imagine a torch shining towards a white screen. Hold a square of thick card in the beam. Then replace it with an equal-sized square of tracing paper, in the same position and orientation. Keep other room lights unchanged so they do not affect the comparison.
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Worked example | Card and tracing paper
The card blocks most of the torchlight that would reach the patch behind it, so the patch looks dark. The tracing paper lets some light through and scatters it, so the corresponding patch can look lighter and its edge may be less distinct.
A suitable answer explains how much light reaches the screen. You can say the card blocks more of the torchlight, so less light reaches the screen behind the card and the shadow is darker.
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Spot the extra change in a weak test
Suppose one square is also moved closer to the torch. The material and position have both changed. That makes it harder to tell which difference caused the result. Repeat the comparison with the same distance from the torch and the same distance from the screen.
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Frequently asked questions
Do I need to use the words opaque and translucent?
The syllabus note does not require those terms for this topic. Explain how much light the material blocks and what reaches the screen.
What can a parent ask during revision?
Ask the child to point to the patch behind each square and explain which patch receives more light.