Unpolarized light passes through two polarizers
whose optical axes are vertical. The intensity of the
emerging light is I0. If a third polarizer is placed
between the polarizers so that its axis is at an angle θ
with the vertical, the intensity of the emerging light is
(A) zero for all θ
(B) I0
(C) I0 cosθ
(D) I0 cosθ^2
(E) I0 cosθ^4
解:注意前两个偏振片平行排列,开始时第二个
偏振片其实不起作用,所以入射光经过第一个偏
振片后强度为I0。加入第三个偏振片后,经过第一
个偏振片后光矢量要进行两次投影,选(E)。