Prism

HOW

1. Set up the prism to observe a coloured band on the ground – the spectrum of sunlight.
2. If the sun is behind the clouds, look at the area through a prism.
3. Rotate it slowly around the horizontal axis.
4. When you stop seeing objects, you see your reflection as in a mirror. This is known as the total internal reflection effect.

WHY

White sunlight is a mixture of different wavelengths, from 400 to 700 nanometres (1 nanometre = millionth of a millimetre). Violet waves are the shortest and red waves the longest. When light enters a prism, and also when it leaves, its waves change direction. Red light refracts the least, violet the most. This phenomenon causes white light to split into different colours in the prism. This is how a rainbow is formed. The role of a prism in nature is performed by raindrops.