Malus's Law

Demonstration of Malus's law – change in the intensity of linearly polarized light passing through a linear polarizer depending on the rotation of the transmission axis of the polarizer.

A halogen lamp powered by alternating voltage is a source of unpolarized light. The first polarizer (with its transmission axis set vertically) transforms it into linearly polarized light.

By inserting a second polarizer into the light path and rotating it, we can demonstrate the change in intensity of the transmitted light according to Malus's law: \( I_{\text{out}} = I_{\text{in}} \cos^2 \alpha \), where \( \alpha \) is the angle between the transmission axes of the individual polarizers.

The experimental setup consists of a halogen lamp, two linear polarizers, and a screen.

The halogen lamp is a source of unpolarized light.

After inserting the first polarizer, we obtain linearly polarized light. Its intensity drops to half. Rotating the polarizer does not change the intensity.

Inserting a second polarizer with the same axis orientation as the first one causes no change.

By rotating, we qualitatively demonstrate Malus's law through the drop in transmitted light intensity.

No light passes through crossed polarizers.