Waves

Malus’ Law

parallel to polariser, the transmitted light has (almost) the same intensity as the polarised light.

Analyser perpendicular to polariser, no transmitted light

With polariser and analyser at some other angle, , the amplitude of the transmitted light waves is equal to component of the amplitude of the polarised light parallel to the plane of the analyser.

Therefore, amplitude of transmitted light is given by

The intensity of a wave is proportional to its amplitude squared so we conclude that if polarised light is incident on a polarising filter the intensity of the transmitted light is proportional to the cos² of the angle between the plane of polarisation and the plane of the filter

where is the intensity of the light incident on the analyser and I is the intensity of the transmitted light.

This is called Malus’ law.

• Waves Chapters Index

• Polarisation of Waves

• Uses of Polarised light