20110209

Physics quiz question: unpolarized light through two polarizers

Physics 205B Quiz 1, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 22.45.

Unpolarized light is incident on two sets of ideal polarizers.


Which set of ideal polarizers have more light transmitted through it?
(A) Set 1.
(B) Set 2.
(C) (Both sets will have the same non-zero amount of light transmitted through them.)
(D) (Both sets will have no light transmitted through them.)

Correct answer: (A)

The fraction of incident unpolarized light passing through the first polarizer in set 1 is 0.5, of which the fraction of vertically polarized light that passes through the second polarizer is (cos(15°))^2 = 0.933, such that light that passes through set 1 is 0.5*0.933 = 0.47.

For set 2, The fraction of incident unpolarized light passing through the first polarizer is 0.5, of which the fraction of horizontally polarized light that passes through the second polarizer is (cos(75°))^2 = 0.0670, such that light that passes through set 1 is 0.5*0.0670 = 0.034.

Student responses
Section 30822
(A) : 4 students
(B) : 0 students
(C) : 4 students
(D) : 0 students

Success level: 50%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

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