The Human Eye and the Colourful World | Activities in Text Book with Solution
Activity 11.3
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?
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| Figure 11.11 An arrangement for observing scattering of light in colloidal solution |
✅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.
Observe
the colour of the transmitted light from the fourth side of the glass tank
facing the circular hole. It is observed at first the orange red colour
and then bright crimson red colour on the screen.