Light fountain

Includes: Indoors, Technology and science

Activity time:
30 mins


Print this activity pack

Let there be light

Try this fun and straightforward demonstration of how fibre-optics work.


  1. Ask the girls to place a 5cm piece of duct tape on the side of the bottle near the bottom to create a ‘patch’ and use the drawing pin to punch a hole in the centre of this.
  2. Stick a piece of masking tape over the hole.
  3. Girls can now fill the bottle with water, before turning on the torch and turning out the lights.
  4. They will need to hold the bottle over a bucket or the edge of a sink. Another member of the group will need to hold the torch on the opposite side of the bottle to the hole.
  5. Ask another member of the group to remove the masking tape.
  6. Ask the girls to think about these questions as they watch the water flow out of the bottle.
    • What happens to the torch light as it comes out of the hole?
    • What happens if they place their hands under the stream of water?
    • If they place the tip of the corkscrew into the hole they have already made and turn it to make the hole a little larger, what happens?

What's happening?

When light hits an invisible barrier between two different materials, it can behave in two different ways. The barrier can partially bend the light (refract) it or it can reflect it.

The light ray inside the stream of water behaves as it would inside an optical fibre. An optical fibre is a flexible, transparent fibre made of glass or plastic, slightly thicker than a human hair. They are used to send information like sounds, pictures or computer code, which travel through the fibres in the form of light.

When you send a light beam into one end of the fibre, it travels along inside and comes out at the other end. It doesn’t matter if the fibre is straight, curved, or bent into loops. The light beam bounces around inside the fibre, reflecting back and forth off the sides, but can’t pass through the walls until it reaches the end. This is called total internal reflection, and it happens just the same way in the stream of water.

Planning checklist

Section Number of girls per adult
Rainbows 5
Brownies 8
Guides 12

How many adults are needed?

Use this calculator to find out the ratio of girls to adults that is required for this activity

2 adults needed