Brewster's Angle: Reflected Light Perfectly Polarized

1 · Predict

At one special angle of incidence (Brewster's angle), light reflecting off a surface becomes perfectly polarized — the reflected beam contains only one polarization direction. Does a higher-index surface have a larger or smaller Brewster angle?

• Larger — a higher refractive index requires a steeper incidence angle to satisfy the Brewster condition.
• A higher index gives a smaller Brewster angle.
• Brewster's angle doesn't depend on the surface's index.

2 · Set Up

1. Open the brewster preset and press Reset. Light travels from air (n₁ = 1.0) toward glass.
2. Enable the Brewster-angle readout.
3. Set the glass's refractive index for each trial and record the Brewster angle.

3 · Collect Data

Plot θ_B (y-axis) against n₂ (x-axis) for your three trials.

4 · Analyze

1. For one trial, compute θ_B = atan(n₂/n₁) using n₁ = 1.0. Compare to the table.
2. Explain why a higher-index surface (n₂ larger) requires a LARGER Brewster angle — steeper incidence — to achieve perfectly polarized reflection.

5 · Extend

1. At Brewster's angle, reflected glare (like off a lake or wet road) is almost entirely horizontally polarized. This is exactly why polarized sunglasses (blocking horizontal polarization) are so effective at cutting glare — they're tuned to block precisely the light that's most strongly reflected at typical viewing angles.
2. At Brewster's angle, the reflected beam contains ZERO p-polarized light (polarized in the plane of incidence) — only s-polarized light reflects. Explain why this means a camera with a polarizing filter, rotated to block s-polarized light, can nearly eliminate reflections off glass or water at this specific angle.

The Physics Behind This Experiment

← Back to experiment