The basics of light reflected through water and how a rainbow is formed has interested children for many years. Creating a simple prism at home will keep you and your children amused for hours, and conducting scientific experiments is an effective way of teaching. This fun experiment describes the science behind how light travels through water to create the beauty of a colourful rainbow. Children will learn about refraction and reflection of light and the formation of the colours of the rainbow.
Fill your plastic sandwich box around to around 3/4 full with clean water and stand this on a flat surface such as a table or worktop. Stick the screen or white card on the wall or prop it up at the end of the container of water.
Put the mirror in the water at the opposite end to where you have the screen. Prop or hold the mirror at an angle in the water. Don't completely submerge the mirror -- leave around half in the water and half out.
Turn on the torch and aim the beam at the centre of the mirror; the reflected beam will travel through the water, which acts as the prism. Look at the screen to see a colourful rainbow. Take some of the water out of the container and see what effect it has on the rainbow.
Change the angle of the mirror and use a different light source to see the varying size and contrast of the image; the brighter the light, the crisper the rainbow will be. Ripple the water with your fingers to get a sparkle effect on your rainbow.