Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 22.45
Unpolarized light passes through two polarizers with polarization axes that can be set at an angle θ with respect to each other. As this angle θ is increased from 0° to 90°, does the amount of light transmitted through the two polarizers increase, decrease, or increase then decrease, or decrease then increase? Explain your reasoning using the properties of light and polarizers. Solution and grading rubric:
- p:
Correct. Amount of light would decrease to zero as θ goes to 90°, whether arguing from "parallel vs. crossed passage" model; and/or Malus' law cos2θ factor in the fraction transmitted through second polarizer, with respect to the 50% that passed through the first polarizer. May misinterpret diagram as depicting θ = 45° as the start, through which the final angle would be θ = 135° ("90° more"). - r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. - t:
Nearly correct, but argument has conceptual errors, or is incomplete. - v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x:
Implementation/application of ideas, but credit given for effort rather than merit. - y:
Irrelevant discussion/effectively blank. - z:
Blank.
Section 31988
p: 12 students
r: 1 student
t: 0 students
v: 0 students
x: 0 students
y: 0 students
z: 0 students
A sample "p" response (from student 7676):
Another sample "p" response (from student 1230), using the diagram as the starting angle to rotate through by 90°:
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