Malus' law

The orientation of an electromagnetic wave is determined by the direction of vibration of the electric field. This is known as the direction of polarization. Depending on the direction of oscillation, we distinguish several types of polarization. If the oscillations of the electric field propagate in the same direction then such a wave is called linearly polarized. Other types of polarization are circular or elliptical polarization. If the field oscillations propagate in opposite directions we speak of an unpolarized wave.

Natural light is not polarized. Light becomes polarized only when it reflects off the surface of transparent insulators such as glass, a sheet of water or a wet roadway, for example.

Naturally occurring polarizers are so-called birefringent crystals, such as calcite (Icelandic spate), tourmaline or mica. We can also achieve polarization with the help of specialized devices called polarizers.

Malus' law is a law discovered by French physicist Étienne Louis Malus - the discoverer of the polarization of light on reflection. Malus' law expresses the dependence of the intensity of linearly polarized light after it passes through an optical polarizer on the intensity of that light before it enters the polarizer.

Malus' Law:

"The intensity of linearly polarized light after passing through an ideal optical polarizer is equal to the product of the intensity of the incident light and the square of the cosine of the angle between the plane of polarization of the incident light and the plane of polarization of the light after passing through the polarizer."



Spectrophotometers are used to study the phenomenon of (measuring) the transmission or reflection of light through a sample.