The prism

What you can do here
  1. Put the prism so that you can see a colourful stripe, the spectrum of the sun’s light on the ground. If it’s cloudy, you can look around you through the prism. You will see various objects with glowing edges. Note the colour of light objects (benches, the nearby sports arena).
  2. Rotate the prism slowly around its horizontal axis. At some angle, you stop seeing things that are behind the prism, but instead you start seeing your own reflection, like in a mirror, this is the effect of total internal reflection.


How does it work
  1. Sunlight consists of waves from 400 to 700 nanometres (1 nm = 0,000001 mm). The human brain perceives the wavelengths as different colours (the colour red is the longest wave while violet is the shortest), and when they are mixed, white is produced. That is why we call sunlight white light. The light going through the air and the prism and then again through the air changes its direction – we say it refracts. The red light refracts the least, the violet – the most, that is why these colours are at extreme positions in white light. The phenomenon of white light dispersion is responsible for the rainbow, with raindrops acting as the prism. The colours of the rainbow are arranged from red in the upper part of the arch to violet on the inside of the arch.
  2. When the light falls on the medium edge between the surfaces at a suitable angle, it does not go through to the other material but gets reflected. This phenomenon is called total internal reflection. The edge becomes a “mirror” in which you can see yourselves.


Interesting facts

The refractive index of the diamond is extremely high which is why it plays unique light tricks.
Sometimes you can see a darker secondary rainbow outside the primary one. The order of colours in the secondary rainbow is reversed.
If the light emitted by various substances is seen through the prism, their chemical composition can be determined (this is called spectral analysis).
Total internal reflection in a set of prisms is used in binoculars to reverse the image.