Question

Which of the following will scatter light and why?

a. Sugar solution b. Soap solution

Answer 1

A soap solution will scatter light because it is a colloidal solution that shows Tyndall effect.

• A colloid is a heterogeneous mixture in which the particles cannot be seen with the naked eye.
• The diameter of the particles of colloids lies in the range of ${10}^{-6}-{10}^{-9}\mathrm{m}$.

Tyndall effect: When the particles can scatter a beam of light passing through them and make the path of light visible.

• The light is scattered when light collides with the colloidal particles and deviates from its normal straight line path.
• This scattering makes the path of the light beam visible, as illustrated below.

Solutions such as sugar solution do not show this effect as the size of particles $(<{10}^{-9}\mathrm{m})$ is so small that they cannot scatter the light.