Tuesday, August 20, 2013

Optical Properties of Colloidal Solution (Tyndall Effect)

Tyndall Effect
Tyndall in 1869, observed that if a strong beam of light is passed through a colloidal solution placed in a dark place and viewed at right angles to the direction of light beam, the path of light shows up as a hazy beam or cone. This is due to the fact that sol particles absorb light energy and then emit it in all directions in space. This emission of light known as Scattering of Light,illuminates the path of beam in colloidal dispersion.
“The phenomenon of scattering of light by the sol particles is called Tyndall Effect. The illuminated beam or cone formed by the scattering of light by the sol particles is often referred as Tyndall Beam or Tyndall Cone. It is not shown by pure solvents.

Explanation
The Tyndall Effect is due to scattering of light by colloidal particles. The colloidal particles first absorb light and then a part of absorbed light is scattered from the surface of the colloidal particles. Maximum scattering intensity being in a plane at right angles to plane of incident light, the path becomes visible when seen from that direction. The particles of pure solvents or true solution are too small to scatter light.

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