Question

The Tyndall effect is observed only when the 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 particles 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 dispersion medium are differing greatly in magnitude.
A) (b) and (c).
B) (a) and (c).
C) (b) and (d).
D) (a) and (d).

Answer 1

We all know that the Tyndall effect is defined as the phenomenon in which the light is scattered by the particles present in the colloid or in a very fine suspension. The scattering of light depends on the frequency of the light and density of the particles.
Example: The water droplets scatter the light, making the headlights beam visible.

Complete step by step answer:
We know that there are two phases in the colloidal particles; they are the dispersed phase and the dispersion medium. The medium in which the colloidal particles are distributed is called the dispersion medium. The phase in which the finely divided particles present is called the dispersion phase.
Let us see some characteristics of the dispersed phase. Size, particle shape, surface charges are the characteristics of the dispersed phase.
We also remember that the color of the dispersion is influenced by the particle size. The radius of the particle and wavelength of light absorbed is inversely proportional to each other. The diameter of the particle is small and it should scatter at a very high wavelength. Thus, the particle size should not be much smaller. And in case of refractive index, when refractive indices of both are the same, the light will not get refracted since both mediums are the same. So the refractive indices have to differ greatly so that light will get refracted.

So, the correct answer is Option C.

Note:
We must remember that the optical properties like the Tyndall effect are used to measure size, shape, and structure, the molecular weight of colloids, light scattering, and turbidity. When light is passed through the dispersed particles, it polarizes the atoms or molecules and forms dipoles. This emits light in all directions and light scattering occurs.