Polarimetry is the study of the rotation of polarized light by transparent substances. Plane polarized light consists of two components rotating in opposite directions. When an optically active substance is placed in the path of plane polarized light, it rotates the plane of polarization. The magnitude of rotation depends on factors like the nature and concentration of the substance, temperature, and wavelength of light. Polarimeters are used to detect and measure optical activity by determining the angle of rotation of plane polarized light passing through a sample.