# Conduct investigations quantitatively using the relationship of Malus’ Law

Hyugens’ model showed that light was a wave.

The phenomena of polarisation helped us understand that light was a transverse wave . A transverse wave has oscillations perpendicular to its direction of propagations. A polariser allows components of oscillations which are parallel to the axis of polariser.

The new lightwave with restricted plane of oscillations is called a Polarised Light

A polariser thus reduces the original intensity to half

If we pass the Polarised light through a second  polariser, with a different axis of polarisation, then the final intensity is given by :-

, where

• I new : the intensity if the emerging polarised light
• I O : the intensity of polarised light falling on the second polariser
• θ = the angle between the axis of the incident polarised light and the axis of the second polariser

To conduct an investigation we would need :

• A light source
• 2 polarising filters
• a light sensor
• Darken the room, and use the light sensor to measure the light intensity produced by the light source
• Place one of the polarising filters in front of the light source and measure the intensity of the polarised light.
• Should be half of original. Refer to this as Io
• Place a second polariser and let the polarised light pass through it.
• Rotate the axis of the second polariser with respect to the first, and measure the intensity of the emerging wave for different angles .

The readings should verify Malu’s Law.

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)