Two plane-polarized beams A and B have mutually perpendicular polarization directions. A polaroid is initially oriented so A is maximum and B is zero. After rotating the polaroid by 30°, the two beams appear equally bright. Find Iₐ/Iᵦ.
Options

Question

Two plane-polarized beams A and B have mutually perpendicular polarization directions. A polaroid is initially oriented so A is maximum and B is zero. After rotating the polaroid by 30°, the two beams appear equally bright. Find Iₐ/Iᵦ.

Options

G1 Physics · Accepted Answer

After the polaroid rotates by 30°, transmitted intensities are Iₐcos²30° and Iᵦsin²30° because the two beams are mutually perpendicular. Equal brightness gives Iₐ(3/4)=Iᵦ(1/4), so Iₐ/Iᵦ=1/3. Option B.