Q.Answer the following question.
What happens when a beam of light is passed through a colloidal sol?

Step 1. Contrast with a true solution. If a beam of light is passed through a true solution, the path of light through it cannot be seen at all -- the solute particles are too small to interact appreciably with the light.

Step 2. What happens in a colloidal sol. When the same kind of light beam passes through a colloidal sol instead, the colloidal particles -- being much larger than a true solution's solute, and comparable in size to the light's wavelength -- scatter some of the light in all directions rather than letting it all pass straight through.

Step 3. The visible result. Because of this scattering, an observer standing at right angles to the beam's original direction can see the beam's path through the sol as a bright, visible cone of light, called the Tyndall cone; this whole phenomenon is called the Tyndall effect. …

• Saying the light is simply 'reflected' rather than scattered in all directions by the particles. …