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Grade 6 Beginner About 10 min Version 1 Awaiting review Premium

Shadows: near and far

Light travels in straight lines. An opaque object, such as card, stops light passing through it, so a dark area forms behind it: a shadow. A translucent object, such as tracing paper, lets some light through, so its shadow is faint. A transparent 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

  1. Place the torch 10 cm, 20 cm and 40 cm from the card and record the shadow's height each time.
  2. 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.