Shadows: near and far
Move a torch closer to and further from an object and watch its shadow on a screen grow and shrink. Try opaque, translucent and transparent objects.
Core concept
In short: Move a torch closer and further away and watch a shadow grow and shrink.
Light travels in straight lines, so an opaque object blocks it and casts a shadow that grows as the light comes closer
Topic: Light
Light travels in straight lines. An opaque: Lets no light through, like wood or a book. All key words object, such as card, stops light passing through it, so a dark area forms behind it: a shadow: A dark shape made where an object blocks the light. All key words. A translucent object, such as tracing paper, lets some light through, so its shadow is faint. A transparent: Lets almost all light through, so you can see clearly through it, like glass. All key words object, such as clear glass, lets almost all light through and casts almost no shadow. Because the rays spread out in straight lines from the torch, the closer the torch is to the object, the bigger the shadow.
What you will learn
- Explain how shadows form because light travels in straight lines.
- Describe how moving the light source changes the size of a shadow.
- Classify materials as opaque, translucent or transparent.
Before you start
- Know that light travels from a source to our eyes.
Materials
- A 5 cm tall card shape, tracing paper and a clear glass slide
Equipment
- Torch, white screen and ruler
Procedure
- Place the torch 10 cm, 20 cm and 40 cm from the card and record the shadow's height each time.
- Replace the card with tracing paper and then clear glass, and compare the shadows.
How this simulation is simplified
- The torch acts as a tiny point of light, so the shadow has sharp edges.
- The object is 5 cm tall and stays 20 cm from the screen.