Tyndall Effect:
When a strong beam of light is passed through a true solution placed in a beaker, in a dark room, the path of the light does not become visible. However, if a beam of monochromatic light is passed through a colloidal solution, placed in the same room, the path of the light becomes visible when viewed from a direction at right angle to that of the incident beam.
This phenomenon was studied for the first time by Tyndall and therefore, it is called Tyndall effect. The cause of Tyndall effect is the scattering of light by the colloidal particles i.e. these particles first absorb the incident light and then a part of it gets scattered by them.