Question

What is especially observed when a beam of light is passed through a colloidal solution?

Answer 1

Colloidal particles can absorb the incident light energy, and these particles act as a source of light energy which scattered the absorbed light in all the direction perpendicular to the beam.

Complete Solution :
Whenever a light beam is passed from a colloidal solution and viewed at right angle, the path of the light beam forms a beam of cone. This phenomenon shows the optical property of colloidal solution which is known as Tyndall effect (the phenomenon of scattering of incident light rays by colloidal particles in all the possible directions).
- When a colloidal particle scatters the absorbed light, these small particles appear as bright spots in the dark background under the ultra-microscope.
Tyndall effect can be observed only, when following two conditions must be satisfied.
- The wavelength of used light should be in the same manner to the Diameter of the dispersed particles.
The reflective indices of the dispersed phase (or discontinuous phase) and dispersion medium (or continuous phase) differ in magnitude.
- The same phenomenon is observed when a beam of sunlight enters a dark room through a small slit. When light rays are focused on a colloidal solution and observed through perpendicular to the beam of light rays, a cone is seen which is called Tyndall cone.

Note: Only sol exhibits the Tyndall effect in which dispersion medium is liquid and dispersed phase is solid.
- Blue sky colour and sea water, passage of sunlight in a dense forest, visibility of projector etc. are the examples of Tyndall effect phenomenon.