Optical properties Tyandall Effect
(i) When light passes through a sol, its path becomes visible because of scattering of light by particles. It is called Tyndall effect. This phenomenon was studied for the first time by Tyndall. The illuminated path of the beam is called Tyndall cone.
(ii) The intensity of the scattered light depends on the difference between the refractive indices of the dispersed phase and the dispersion medium.
(iii) In lyophobic colloids, the difference is appreciable and, therefore, the Tyndall effect is well - defined. But in lyophilic sols, the difference is very small and the Tyndall effect is very weak.
(iv) The Tyndall effect confirms the heterogeneous nature of the colloidal solution.
(v) The Tyndall effect has also been observed by an instrument called ultra – microscope.
Some example of Tyndall effect are as follows
(a) Tail of comets is seen as a Tyndall cone due to the scattering of light by the tiny solid particles left by the comet in its path.
(b) Due to scattering the sky looks blue.
(c) The blue colour of water in the sea is due to scattering of blue light by water molecules.
(d) Visibility of projector path and circus light.
(e) Visibility of sharp ray of sunlight passing through a slit in dark room.