Question

Why Sodium light used in polarimeters?

Answer 1

Polarimeter:

1. A polarimeter is a scientific instrument in which the polarization of light can be measured and determines the effect of a substance in rotating the plane of polarization of light.
2. Polarimeters compute the optical activity by passing monochromatic light through two polarizing plates.
3. Sodium light is used because it produces monochromatic light of $589nm$ and the energy output is high.
4. Most of the polarimetric data have a sodium yellow emission at $589nm$ as early light sources were either fire flames or sunlight.

Polarization:

1. Light waves contain multiple planes of vibrations.
2. When the light wave has vibrations in several planes, it is called unpolarized light.
3. Now, we can restrict the vibration to specific planes.
4. When the light has only one plane of motion, that is called polarized light.
5. Polarization of light is the process of converting unpolarized light into polarized light.
6. The angle of incidence that produces a 90° angle between the refracted and reflected light wave is called the Brewster angle.
7. Brewster’s law formula, $\mu =\tan i$ Where, $\mu$ is the refractive index of the material and $i$ is the polarization angle.
8. The following diagram signifies the polarization of light.

Therefore Sodium light is used in polarimeters.