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 using a polarimeter.


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.