Question

Why Sodium light used in polarimeters?

Answer 1

Hint: A polarimeter is defined as a scientific device that is used for measuring the angle of rotation caused by the passage of polarized light through an optically active substance. Polarimeters measure optical activity by passing monochromatic light through two polarising plates, creating a polarized beam.

Complete answer:
A polarimeter is a device used to measure the angle of rotation caused by the passing of polarized light through an optically active substance. Sodium Lamps are used in a polarimeter because it gives off monochromatic light wavelength 589 nanometres. Sodium lamps also give high-energy output. It can also give High sensitivity and S/N ratio. The sodium lamp produces a line spectrum meaning that it gives monochromatic light of 589 nanometres
We also use sodium for another reason. Most of the polarimetric data exists with the sodium yellow emission at 589 nanometres because sodium lamps were among the most common and efficient ones when electricity was rather new. Early light sources were either fire flames or sunlight. Generation of sodium light is also very easy. Sodium emission can be obtained by introducing salt in the flame.
Another important thing to note is that optical rotation is a function of the refractive index of the material and refractive index is strongly dependent on the wavelength of light used.

Note:
We can also use mercury lamps in some particular cases. Mercury (Hg) lamps can be used as light sources for a polarimeter because they produce many emission lines from the ultraviolet to the visible region. The wavelength of the mercury green line at 546.1 nanometres is also used. It is possible to perform measurements at different values in combination with appropriate optical filters.