Walker, Halliday & Resnick — Electromagnetic Waves: Problem 17

17 A beam of partially polarized light can be considered to be a mixture of polarized and unpolarized light. Suppose we send such a beam through a polarizing filter and then rotate the filter through 360° while keeping it perpendicular to the beam. If the transmitted intensity varies by a factor of 4.0 during the rotation, what fraction of the intensity of the original beam is associated with the beam’s polarized light?