Fig. 11.11 shows an experimental set up for observing a phenomenon of light in colloidal solutions. A student dissolves about 200 g of sodium thiosulphate (hypo) in about 2 L of clean water in the tank and adds about 1 to 2 mL of concentrated HSO4 to the water. What would he observe after the source of light S is switched on (i) from the three sides of the glass tank? (ii) from the fourth side of the glass tank facing the circular hole ? Give reason.

Fig. 11.11 shows an experimental set up for observing a phenomenon of

1.	Fig. 11.11 shows an experimental set up for observing a phenomenon of light in colloidal solutions. A student dissolves about 200 g of sodium thiosulphate (hypo) in about 2 L of clean water in the tank and adds about 1 to 2 mL of concentrated HSO4 to the water. What would he observe after the source of light S is switched on (i) from the three sides of the glass tank? (ii) from the fourth side of the glass tank facing the circular hole ? Give reason.
Answer» Solution :(i) From three sides of the glass tank blue LIGHT is obtained due to scattering of light of short wavelengths by MINUTE colloidal sulphur particles. (ii) From the fourth side of the glass tank facing the circular hole, first the orange-RED and then BRIGHT crimson red coloured light is observed. It is due to the FACT that red light of longer wavelength suffers very little scattering and travels straight through the tank.