Polarization

AP Physics 2 EK 14.3.A.2.i: transverse waves can be polarized and oscillate in a single plane. EK 14.3.A.2.ii: longitudinal waves cannot be polarized. That pair is the reason polarization is in the course at all. Light can be polarized, so light is transverse. Sound cannot, so sound is not.

How a wave gets polarized. EK 14.3.A.2 says transverse waves that are reflected from a surface, refracted through a medium, or pass through specific openings may be polarized.

Intensity. EK 14.3.A.3 says polarization of a wave may result in a reduction of the wave's intensity, and 14.3.A.3.i and ii define intensity as the average power transferred per unit area over one period of the wave. The CED stops there, but the standard result follows from that description: unpolarized light is an even mixture of every orientation, so an ideal polarizer passes half of it, $I = I_0/2$, whatever angle the filter is set to. Only after the first filter does the relative angle between filters start to matter.

On the formula. The CED requires only the qualitative reduction, and the AP Physics 2 equation sheet prints no law of Malus. Expect to argue that intensity falls, and that crossed filters pass nothing, rather than to compute an angle.

Polarizing light changes neither its frequency nor its wavelength, only its amplitude and its orientation.