Question

The conditions given below are in the context of observing Tyndall effect in colloidal solutions:

1. The diameter of the colloidal particles is comparable to the wavelength of light used.
2. The diameter of the colloidal particles is much smaller than the wavelength of light used.
3. The diameter of the colloidal particles is much larger than the wavelength of light used.
4. The refractive indices of the dispersed phase and the dispersion medium are comparable.
5. The dispersed phase has a very different refractive index from the dispersion medium.

Choose the most appropriate conditions from the options given below:

Options

• (B) and (E) only

• (C) and (D) only

• (A) and (E) only

• (A) and (D) only

Answer 1

(A) and (E) only.

Explanation:

Light scattering is the foundation of the Tyndall effect. The scattering and consequently the Tyndall effect are reduced by smaller diameters and similar magnitudes of refractive indices. If the diameter of the dispersed phase particle smaller than that of wavelength of light used then the scattering of light will not occur. Therefore, the diameter of the dispersed particles should be equal or not much smaller than the wavelength of the light used.

The ratio of the speed of light in a material to the speed of light in any medium is known as the refractive index. To scatter light and see the Tyndall effect, the refractive indices of the dispersed phase and the dispersion medium should differ in magnitude more. The scattering of light will not take place and the Tyndall effect cannot be observed if the refractive indices of the dispersed phase and dispersion medium are equivalent in magnitude.

Therefore, the appropriate conditions for Tyndall effect are:

(A) The diameter of the colloidal particles is comparable to the wavelength of light used.

(E) The dispersed phase has a very different refractive index from the dispersion medium.