Polarisation

Filters, sunglasses and a paradox

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Polarisation is the direction the electric field oscillates.
• Unpolarised light: a polariser passes half. Polarised light: $I = I_0\cos^2\theta$.
• A middle polariser at 45° lets 1/8 through two crossed polarisers.

Steps

1. Which way does it wiggle?
2. Two wiggles, one pattern
3. Two polarisers
4. The three-polariser paradox
5. Thirty degrees
6. Thirty degrees apart
7. Polarised sunglasses