• summary_type: concept
• word_count: 170

Polarization proves light is a transverse wave. Unpolarized light has random electric field directions perpendicular to propagation. A polarizer (Polaroid) transmits only the component along its axis, reducing unpolarized intensity $I_{0}$ to $I_{0}$/2. Malus's law: when polarized light passes through an analyzer at angle θ, I = $I_{0}$c$os^{2}$θ. Two crossed polaroids (θ = 90°) transmit zero light. Inserting a third polaroid at 45° between crossed polaroids allows $I_{0}$/8 to pass — a classic JEE problem. Brewster's law: tan i_B = n_{2}/n_{1} gives the angle at which reflected light is completely polarized (perpendicular to the plane of incidence). At Brewster's angle, reflected and refracted rays are perpendicular. Polarization also occurs by scattering (90° scattered light is fully polarized) and by double refraction in birefringent crystals. Quarter-wave plates convert linear to circular polarization; half-wave plates rotate the polarization plane.