Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 23.97
[10 points.] A beam of light strikes an air-oil interface with an incident angle of 41°. The beam travels through the oil and emerges from a parallel oil-glass interface below. Ignore reflections, and this diagram is not drawn to scale.
Is the angle of the exiting ray in glass greater than, less than, or equal to 41°? Explain your reasoning using the properties of light and refraction.Solution and grading rubric:
- p = 10/10:
Correct. Solves for theta_3 after first solving for theta_2 using Snell's law twice; or solves for theta_3 by noting that the oil layer can be ignored mathematically in n_1*sin(theta_1) = n_3*sin(theta_3); or argues that since the indices of refraction increase, the angles will decrease such that theta_3 > (theta_2) > theta_1. - r = 8/10:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. - t = 6/10:
Nearly correct, but argument has conceptual errors, or is incomplete. - v = 4/10:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 2/10:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1/10:
Irrelevant discussion/effectively blank. - z = 0/10:
Blank.
Grading distribution:
Section 30882
Exam code: midterm01g74S
p: 8 students
r: 0 students
t: 0 students
v: 0 students
x: 0 students
y: 0 students
z: 0 students
A sample "p" response (from student 7503), eliminating n_2*sin(theta_2) in the two Snell's law equations:
A sample "p" response (from student 3373), explicitly solving for theta_2, and then for theta_3:
A sample "p" response (from student 1990), arguing qualitatively for theta 1 > theta_2 > theta_3:
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