Polarization | Malus's Law 3D Simulation

About this simulation

Polarisation shows unpolarized light meeting a polarizer and then an analyser. The wiggly lines are the electric field, with amplitude proportional to the square root of intensity. Students rotate the analyser from 0 to 180 degrees, and can add a middle filter at its own angle to show that a third filter can let light through crossed filters. Readouts give the final intensity, the intensity after the first filter and the last angle difference. It demonstrates Malus's law and the transverse nature of light.

What students can explore

Rotate Analyser angle to 90 degrees and see the light disappear.
Set the analyser to 0 and read the After 1st filter value.
Set Analyser angle to 90, turn on Add middle filter and set Middle filter angle to 45.
Move the middle filter angle and find the setting that lets the most light through.
Compare Intensity out at 30, 45 and 60 degrees with I0 times cos squared theta.

Learning objectives

1State Malus's law and use it to find transmitted intensity.
2Explain why unpolarized light loses half its intensity at the first filter.
3Describe light as a transverse wave with an electric field.
4Explain why a third filter can restore light between crossed filters.

Questions teachers ask

Is the Polarization simulation free?

Yes. It is free to use, needs no sign-up and runs in any modern browser, including whiteboards, tablets and Chromebooks.

Why does a middle filter let light through crossed filters?

The middle filter rotates the polarization direction by an angle. Light then has a component along the final axis, so some intensity passes, even though the first and last filters are crossed.

How do I use it?

Drag the analyser angle, then switch on the middle filter and set its angle. Watch the field wiggles shrink and read the Intensity out value.

What is Malus's law?

It says the intensity of polarized light after an analyser is I0 times cos squared of the angle between the light's polarization and the analyser axis.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

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