Question

Tyndall effect in colloidal solution is due to:
(A) Absorption of light
(B) Scattering of light
(C) Reflection of light
(D) Presence of electrically charged particles

Answer 1

Hint: When light beams are passed through a colloidal solution, they deviate from their original path and make the new path visible through the solution.

Complete step by step answer:
-The Tyndall effect is a phenomenon where the particles of a colloid scatter the light beams which are directed towards them. Tyndall effect occurs in colloidal solutions and very fine suspensions also. This effect is also known as Willis-Tyndall scattering.
The intensity of the scattered light depends on the density of the colloidal particles and the frequency of the light.
-Basically when we pass a beam of light through a colloid, the particles present in this colloidal solution will not allow the light beam to completely pass through it. The light beam will collide with the colloidal particles and get scattered (deviate from its original path). This scattering of light makes its path visible inside the solution.
John Tyndall was the first one to discover this phenomenon.

Examples of Tyndall effect:

 1) Milk is a colloid of fat and protein globules. So a beam of light through it gets scattered.
 2) If we switch on a torch in a foggy environment the light path becomes visible because here small water droplets in the environment will act as colloidal particles.
-Also a clear sky appears blue because of scattering of light by the particles present in the air.
-To cause scattering of light the size of the particles should be between 40-900 nm (which is below or near the wavelength of visible light).

-Scattering due to Tyndall effect is quite similar to a phenomenon known as Rayleigh scattering, according to which intensity of scattered light is inversely proportional to fourth power of its wavelength.

Hence, the correct answer is option B.

Additional Information
Our eyes show different colours like blue, black, brown or green due to the amount of melanin in one of the iris layers. For a blue coloured eye the amount of melanin present is relatively lower as compared to the black eye which makes the iris quite translucent. Hence when light is incident on this translucent layer it gets scattered. Since blue light is scattered most this iris appears blue.

Note:
A light beam having smaller wavelength (or we can say higher frequency) are more scattered. They experience a more prominent Tyndall effect. So, generally blue light is more scattered than red light (blue colour has smaller wavelength). This is why the smoke released from automobiles sometimes appears blue.