Tyndall effect

• A. The reflection of light by a colloid
• B. The dispersion of light in a solution
• C. The rate of light absorption by a colloid
• D. Scattering of light by colloids

Answer: (D)

The Tyndall effect is the scattering of light by particles in a colloid. When a beam shines through a colloidal mixture, the dispersed particles are large enough to scatter visible light, making the path of the beam visible inside the sample (and sometimes in the surrounding air). This scattering occurs because the particle sizes are comparable to the wavelength of light, which is typical for colloids but not for true solutions. That’s why you can often see a visible beam in a colloid, whereas in a true solution the particles are too small to scatter light noticeably.

The other ideas don’t fit as well: reflection is just light bouncing off surfaces, not scattering within the medium; dispersion can refer to the spreading of light or of a mixture, not the light being scattered by colloidal particles; and the rate of light absorption describes how much light is taken up by the material, not how the light is scattered.