<P> Polarization by reflection was discovered in 1808 by Étienne - Louis Malus (1775--1812). (See also Optical rotation #History). A nicol prism or a polaroid lens can be used to polarize the light . </P> <P> The ratio, the purity, and the concentration of two enantiomers can be measured via polarimetry . Enantiomers are characterized by their property to rotate the plane of linear polarized light . Therefore, those compounds are called optically active and their property is referred to as optical rotation . Light sources such as a light bulb, a light - emitting diode (LED), or the sun emit electromagnetic waves at the frequency of visible light . Their electric field oscillates in all possible planes relative to their direction of propagation . In contrast to that, the waves of linear - polarized light oscillate in parallel planes . </P> <P> If light encounters a polarizer, only the part of the light that oscillates in the defined plane of the polarizer may pass through . That plane is called the plane of polarization . The plane of polarization is turned by optically active compounds . According to the direction in which the light is rotated, the enantiomer is referred to as dextro - rotatory or levo - rotatory . </P> <P> The optical activity of enantiomers is additive . If different enantiomers exist together in one solution, their optical activity adds up . That is why racemates are optically inactive, as they nullify their clockwise and counter clockwise optical activities . The optical rotation is proportional to the concentration of the optically active substances in solution . Polarimeters may therefore be applied for concentration measurements of enantiomer - pure samples . With a known concentration of a sample, polarimeters may also be applied to determine the specific rotation when characterizing a new substance . The specific rotation (α) λ T (\ displaystyle (\ alpha) _ (\ lambda) ^ (T)) is a physical property and defined as the optical rotation α at a path length l of 1 dm, a concentration c of 1g / 100 mL, a temperature T (usually 20 ° C) and a light wavelength λ (usually sodium D line at 589.3 nm): </P>

What is the difference in working of bi-quartz polarimeter and nicol prism