1) Take a metal tray and fill it with water.
2) Place a mirror in the water such that it makes an angle with water surface.
3) Now focus white light on the mirror through the water as shown in figure.
4) Keep a white card board sheet above the water surface.
5) We can observe the colours VIBGYOR on the board.
6) The splitting of white light into different colours (VIBGYOR) is called dispersion.
7) So consider a white light is a collection of waves with different wavelength.
8) Violet has shortest wavelength and red has longest wavelength.