The Electromagnetic Spectrum
Light Sound and Waves

Eerie Blue Water

Enrichment Activity for 5-11 11-14

What you need

  • Two clear glasses
  • Tap water
  • Tonic water
  • Dark paper


  1. Fill one glass with tap water and the other with tonic water and put them both in direct sunlight
  2. Holding the dark paper behind them, but not blocking the light, look across the surfaces of the water

Results and Explanation

The tonic water will be giving off an eerie blue glow! Tonic water contains quinine. The quinine absorbs ultraviolet light from the Sun and re-emits it as visible blue light.

IOP DOMAINS Physics CPD programme

Electricity CPD videos

Our new set of videos gives teachers and coaches of physics a preview of the training we offer ahead of this term's live support sessions.

Find out more