Place a strong source (S) of white light at the focus of a converging lens (L1). This lens provides a parallel beam of light.
Allow the light beam to pass through a transparent glass tank (T) containing clear water.
Allow the beam of light to pass through a circular hole (c) made in a cardboard. Obtain a sharp image of the circular hole on a screen (MN) using a second converging lens (L2), as shown in Fig. 11.11.
Dissolve about 200 g of sodium thiosulphate (hypo) in about 2 L of clean water taken in the tank. Add about 1 to 2 mL of concentrated sulphuric acid to the water. What do you observe?
✅Answer: Fine microscopic sulphur particles precipitate in 2 - 3 minutes. As a result, blue light can be observed from the three sides of the glass tank. This is due to scattering of short wavelengths by colloidal sulphur particles.