Question

In an experiment to study the scattering of light by passing a beam of white light through a colloidal solution of sulphur in a transparent glass tank:
(a) Which colour is observed from the front of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset?
(b) Which colour is observed from the sides of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset?

Answer 1

Hint: Recall the phenomenon of scattering of white light. Also, recall the concept of Tyndall effect. Compare the size of the sulphur particles in the colloidal solution in the transparent glass tank with the wavelengths of the different colors of light in the white light. Hence, determine which colour of light is scattered the most and the least.

Complete answer:
The phenomenon in which a white ray of light is scattered by the particles of colloidal particles is known as Tyndall effect. In the experiment to study the scattering of light, a beam of white light is passed through the colloidal solution of sulphur in a transparent glass tank.
The white light passed in the transparent glass tank gets scattered by the sulphur particles in the colloidal solution.

(a) The size of the colloidal sulphur particles in the solution in the tank is approximately the same as the wavelength of the blue light. Hence, the blue light in the white light is scattered the most by the colloidal sulphur particles than any other colour in the white light.

Hence, the blue colour of light is observed when the transparent glass tank is observed from the front of the glass tank which corresponds to the colour of sky on a clear day.

(b) The size of the colloidal sulphur particles in the solution in the tank is much smaller than the wavelength of the red light. Hence, the red light in the white light is scattered the least by the colloidal sulphur particles than any other colour in the white light.

Hence, the red colour of light is observed when the transparent glass tank is observed from the sides of the glass tank which corresponds to the colour of sky around the sun at sunset.

Note: The students may think that the wavelength of the violet color of light in the white light is smallest among all the colours of light then why blue colour is scattered the most. But the students should keep in mind that there is less violet light in white light and human eyes are less sensitive to violet colour of light.