Question

The tyndall effect is observed only when following conditions are satisfied:
(a) The diameter of the dispersed particles is much smaller than the wavelength of the light used.
(b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
(c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude.
(d) The refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude.

(A) (b) and (c)
(B) (a) and (c)
(C) (b) and (d)
(D) (a) and (d)

Answer 1

Tyndall is basically the scattering of light by the colloidal particles and depends on the diameter of dispersed particle and refractive indices of dispersed phase and medium. Smaller the diameter and similar the magnitude of refractive indices, lesser is the scattering and hence the tyndall effect and vice-versa.

Complete step by step answer:
Firstly, we should know what the Tyndall effect is. The phenomenon of scattering of light by colloidal particles as a result of which the path of the beam becomes visible is called a tyndall effect. It is not observed in the true solutions because the particles of true solution are very small to cause any scattering of light.
It was first observed by Faraday and later on studied by Tyndall and hence, it is named as Tyndall effect.
The Tyndall effect would be possible only if the following two conditions are satisfied. They are:
1. The diameter of the dispersed phase particles (i.e. the components present in small proportions and is just like the solute in a solution. E.g. colloidal solution of silver in water, in which the silver is a dispersed phase.) should not be smaller than the wavelength of light used because they won’t be able to scatter the light so, therefore, the diameter of the dispersed particles should be equal or not much smaller than the wavelength of the light used.
2. The refractive indices (i.e. the ratio of the velocity of light in vacuum to the velocity of light in any medium) of the dispersed phase and the dispersion medium (the component present in excess and is just like the solvent in the solution. E.g. colloidal solution of silver in water in which water acts as dispersion medium.) should differ greatly in magnitude than only the particles will be able to scatter the light and tyndall effect will be observed. On the other hand, if the refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude, then there will be no scattering of light and hence, therefore, no tyndall effect is observed.
So, from the above given statements, the statements (b) and (d) are correct.

Hence, option (C) is correct.

Note: Tyndall effect is used to distinguish between a true solution and a colloidal solution. when a beam of light is passed through the solution, if the path of light gets illuminated, the solution is called colloidal. On the other hand, if the path of light does not get illuminated, it is called a true solution.