## 20180324

### Physics midterm question: different light polarizations, same polarizer set

Physics 205B Midterm 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

A set of two polarizers has either (a) horizontally polarized light, or (b) vertically polarized light incident on it. Discuss why this set of two polarizers will pass through the same fraction of horizontally polarized and vertical polarized light. Explain your reasoning using the properties of light and polarization.

• p:
Discusses/demonstrates that the same amount of light will pass through the set of polarizers as:
1. the horizontally polarized light is at an angle of 45° with respect to polarizer 1, resulting in cos245° = (1/2) of this passing through, with a 45° polarization angle parallel to that of polarizer 1; and
2. the vertical polarized light is also at an angle of 45° with respect to polarizer 1, resulting in cos245° = (1/2) of this passing through, also with a 45° polarization angle parallel to that of polarizer 1; then
3. since for both cases (initially horizontally polarized light or initially vertically polarized light) the light that has passed through polarizer 1 has the same polarization angle and intensity, after passing through polarizer 2 the amount of light (and polarization direction) will be same for both cases.
• 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.
Sections 30882, 30883
Exam code: midterm01cVdP
p: 26 students
r: 3 students
t: 4 students
v: 0 students
x: 0 students
y: 0 students
z: 0 student

A sample "p" response (from student):