How to bend light with water

  • 05 Apr 2013
Chris Clancy


Amaze people by trapping a beam of light inside a stream of water, then bending it to your will. Kathy Ceceri, senior editor of the GeekMom blog at and co-author of Geek Mom: Projects, Tips, And Adventures For Moms and Their 21st-Century Families, explains how to mimic fibre-optics using household materials.

You'll need

A sink or container to catch the water

A clear, smooth-sided two-litre plastic bottle with cap

A cheap laser pointer

A rubber band

A permanent marker

A metal nail

1. Set up the laser pointer

Light bends as it crosses the boundary between materials of different density. Start by turning the laser pointer on. If necessary, wrap the rubber band around the on/off button so it stays on. Lay the pointer on a box or cup so it's level, about ten centimetres above the counter.

2. Prepare the bottle

Fill the bottle with water and replace the cap tightly. Shine the pointer so the light passes through. Mark where the beam touches the far side of the bottle and make a hole through the mark with the nail. (It won't leak until you loosen the lid.)

3. Now bend the light

Dim the lights. With the pointer aimed at the hole, unscrew the cap just enough to let out a thin stream of water. The beam should travel straight through the bottle and curve downwards with the stream. You may need to adjust the laser or move the bottle to get the best effect.