optical activity

rotation of the plane of polarization by an optically active substance

Optical activity demonstrated cane-sugar solution.

Optical activity is the property, possessed by certain substances, of rotating the plane of polarization of polarized light passing through them. This optical rotation is measured by polarimetry. Optical activity is shown by asymmetric crystals which have two mirror-image forms – the rotation being to the left (levorotatory, l-) or right (dextrorotatory, d-) respectively – and by compounds with asymmetric molecules showing optical stereoisomers. Magnetic rotation of the plane of polarization is known as Faraday rotation.