The Polariser

Light is a transverse wave: its electric field oscillates across the direction of travel. A polariser passes only the field component along its axis, so through a rotated analyser the intensity follows Malus’s law, I = I₀·cos²θ. Drag the dial on the bench, or use the slider.

Bench

Analyser angle θ 0°

Detector — transmitted intensity

I / I₀ = 1.000 cos²θ = 1.000

P1 fixed at 0° polarises the unpolarised source — it transmits exactly ½ the incident intensity. After P1 we call that I₀. The analyser at θ then passes I₀·cos²θ: full at 0°, dark at 90°.

Look

Drag the analyser dial on the bench to rotate it · or use the slider. Hit Sweep to watch the screen breathe through a full rotation. The screen brightness behind the last filter is the computed intensity, exactly.