Question

Tyndall effect is shown by:
A) particles in colloidal solution.
B) particles in a very fine suspension
C) large particle like stones
D) both A and B

Answer 1

Hint: Tydall effect is scattering of light by particles of a mixture. Only the mixtures having solid particles of size comparable to that wavelength of light can scatter light and thus show Tyndall effect. Wavelength of visible light is approximately between 380 nanometer to 700 nanometer.

Complete Step By Step Solution:
Tyndall effect is the process of scattering of light in colloidal or very fine suspended solutions. In this effect, the light beam is scattered by the particles suspended in colloid solution.
Colloidal solutions are the solution in which particles of one medium having size range between 1 nanometer to 1000 nanometer are dispersed in another medium. Substance whose particles are suspended is called a dispersed phase while the medium in which they are suspended is called continuous phase. Suspensions are the mixture containing solid particles large enough for sedimentation.
When light passes through a solution, it does not deviate from its path and travel out of the solution. But when light passes through a colloidal solution it gets scattered by the suspended particle and deviates from its original path. This scattering of light makes the path of light visible. This happens because the size of a particle becomes comparable to the wavelength of visible light. Since the wavelength of blue light is smallest (compared to other visible light), it gets scattered more than any other visible light.
Tyndall effect is shown by colloidal solutions and some very fine suspension. Suspensions usually have large sized particles, so they do not show Tyndall effect, but some very fine suspensions do show this effect. Some examples of mixtures showing Tyndall effect are-
Milk which is a colloid containing fat.
Mixture of flour and water which is a suspension.
Hence the correct option is D.

Note: Not all suspensions show Tyndall effect, only the one in which solid particles are small enough to scatter light, show this effect. The Tyndall effect was first discovered by British physicist John Tydall. In solutions the size of solid particles is too small to scatter light. So they do not show Tydall effect.