Question

The phenomenon of rotation of plane polarized light is called:
A. Kerr effect
B. Double refraction
C. Optical activity
D. Dichroism

Answer 1

Hint: Plane polarized light vibrates only in a single direction. We can polarize the light with the help of a polarizer. We can use this plane polarised light for the polarimetry. It helps to study how the chemical compound interacts with the plane polarised light.

Complete step-by-step answer:
It is better to understand what plane polarised light before answering the question. An unpolarized light contains a large number of atoms producing waves with particular orientation with the electric vector E. So the resultant wave is the superposition of light waves vibrating in all directions. Polarization is mainly done to transform the unpolarized light to the polarized one. In this case, we will block the electric field vector in a particular plane. Hence the vibration occurs only in a single plane, all other vibrations are limited. The plane normal to the plane of vibration is known as the plane of polarization.

The optical activity can find out from the magnitude of the rotation of the plane of polarized light. Optically active polarimetry is a method that measures the interaction between a compound and plane-polarized light. This measures the rotation of the polarized light as it passes through an optically active compound. This technique can measure the direction of vibration of polarized light when interacting with an optically active compound. A substance is said to be optically active if it rotates the plane of polarization of polarized light. The substance that can rotate the plane to the clockwise direction is known as dextrorotatory and the substance which can rotate the plane of polarization counterclockwise is known as levorotatory. Chiral compounds are the reason behind this rotation of plane-polarized light.
So the correct option is C.

Additional information:
The magnitude of rotation of optical activity depends on;
1. Nature of the substance
2. Length of the liquid column through which the light passes
3. The temperature of the solution
4. The wavelength of the light
5. The concentration of the solution

Note: Optically active substances can find out by using polarized light. Double refraction occurring when light ray incident on the birefringent materials. It is split by polarization into two rays and they will take different paths. Dichroic materials used for the polarization by absorption. This material can absorb more light in a specific plane than other planes. So the light can be polarized. Kerr effect is the phenomenon in which the material refractive index will change according to the electric field that we are applying.