Polarization of light
Light is a transverse wave whose electric field can oscillate in any direction perpendicular to its motion; polarizing it restricts that oscillation to a single direction.
Practise this conceptLight is a transverse wave, meaning its electric field oscillates perpendicular to the direction it's travelling — but perpendicular still leaves a full circle of possible directions to oscillate in, and ordinary light is a jumbled mix of all of them at once. Polarizing it means restricting that oscillation to just one direction.
Any transverse wave can be polarized in principle, not just light — the idea applies equally to a shaken rope, restricted to wiggling only up-and-down by a narrow slot. Longitudinal waves like sound can't be polarized at all, because there's only one direction available to them to begin with, along their direction of travel.
A polarizing filter works by absorbing light oscillating in every direction except the one aligned with its transmission axis, not by picking out a single colour — that's why stacking two polarizing filters at right angles to each other blocks light almost completely, regardless of the light's colour, while lining them up lets it through.
Key ideas
Requires: Wave properties: amplitude, wavelength and frequency
Formulas
| Symbol | Name | Unit |
|---|---|---|
| intensity | W/m^2 (watt per square metre) | |
| intensity | W/m^2 (watt per square metre) | |
| angle | deg (degree) |
Common misconceptions
- Only light can be polarized; other transverse waves cannot.
- Polarized light has a lower energy than unpolarized light of the same intensity.
- Polarizing filters work by absorbing all the light except one exact color.