Light, Sound and Waves

Reappearing Coin

Enrichment Activity for 5-11 11-14

What you need

  • Coin
  • Mug
  • Jug of water
  • Blu Tack
  • A friend


  1. Stick the coin to the bottom of the empty mug
  2. Step back, or move your head, until you can no longer see the coin in the mug
  3. While you stay in position, get your friend to slowly pour water into the mug

Results and Explanation

The coin reappears because the water bends, or refracts, the light travelling from the coin so that it can now reach your eye.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.

can be represented by Ray Diagrams
formalised by Snell's Law
has the special case Total Internal Reflection
is used in analyses relating to Lens
can be analysed using the quantity Refractive Index
can be exhibited by Progressive Wave
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