Arrow illusion - exploring refraction with water and markers

Free Science Experiments -

Arrow illusion - exploring refraction with water and markers

I have been looking for ways to extend our exploration of light and refraction since we started to play with light with the Rainbows & Light Science Kit.

This experiment is simple, super easy to do and uses items you very likely already have at home. It is a fantastic way to visualise light refraction and understand that what we see is not always what is actually in front of us!


Simple items needed to conduct an experiment on light refraction

  • Marker
  • Paper
  • Clear glass
  • Jug or second glass
  • Water


  1. Fold the paper in half to make a tent.
  2. Draw a small arrow with the marker on one side of the paper about a third of the way from the fold.
  3. Place the glass in front of the arrow.
  4. Fill the glass with water and watch as the arrow magically changes direction!

The Science

This optical illusion can be explained by light refraction. When light passes through a material such as water it refracts (bends). When the light hits the water it refracts inwards. This point at where this light meets is called the focal point. The light rays cross over beyond the focal point. This means the light originally on the left is now on the right and vice versa which causes the arrow to appear like it’s pointing in the opposite direction to what it really is.

If you have science loving kids, don't forget to check out the Chemistry-in-Action kit. It comes with everything you need to explore chemistry safely at home.

Exploring refraction with arrows, water and sunlight

As a bonus, the glass and water created the conditions for separating white light into its component colours making a rainbow!


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