Tyndall effect is observed when:
(1) The diameter of dispersed particles is similar to the wavelength of light used.
(2) The refractive index of dispersed phase is greater than that of the dispersion medium.
(3) The diameter of dispersed particles is much smaller than the wavelength of light used.
(4) The diameter of dispersed particles is much larger than the wavelength of light used.
Correct answer: (1) The diameter of dispersed particles is similar to the wavelength of light used.
Explanation:
The diameter of the dispersed particles is not much smaller than the wavelength of the light used *The intensity of scattered light depends on the difference between the refractive indice of the D.P and D.M., In lyophobic colloids, this difference is appreciable and therefore the tyndal effect is quite well defined but in lyophilic sols the difference is very small and the tyndal effect is very weak. So, to show Tyndall effect the refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.