Trick of the light

A favourite interactive display at Otago Museum’s Science Centre is Light Island, where you can play with colours and light to reflect it and refract it.

This very cool experiment with light looks like an amazing magic trick! We are going to use light refraction in a simple experiment with a big ‘wow’ factor. 


  • Paper 
  • Glass or glass jar 
  • Pens 
  • Water 


  1. Fill the glass with water, almost to the top. 
  2. Draw an arrow on the paper. 
  3. Place the paper behind the glass and watch. 

The arrow changes direction! 

In this experiment, we are using the scientific concept of refraction, which is the bending of light. Refraction occurs when light travels from one medium to another, like from air to water or water to air. 

During the experiment, the light travels from the image through the air, then through the glass into the water, and finally out of the glass and into the air once more before it reaches our eyes. Light refracts as it passes from one medium to the next because it travels at different speeds through those mediums. In this experiment, light bends once when it goes through the glass into the water and then again when it comes out of the glass into the air. As a result, the light paths cross, and the image appears to be flipped. Amazing!

For more amazing science, come and visit the Otago Museum. We are more than a museum and are home to the biggest science centre in New Zealand.