Physics quiz question: reflection phase shifts

Physics 205B Quiz 3, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 25.17

A thin layer of MgF_2 (n = 1.38) is coated over glass (n = 1.48). Light that reflects off the top of the coating has a phase shift of __________, while the light that reflects off the bottom of the coating (and the top of the glass) has a phase shift of ___________.
(A) 0°, 0°.
(B) 0°, 180°.
(C) 180°, 0°.
(D) 180°, 180°.

Correct answer: (D)

Light in air reflects off of the top of the film with a 180° phase shift ("fast off of slow"). Light in the film reflects off the top of the glass with a 180° phase shift as well (also "fast off of slow"). (The two reflections are thus in phase with respect to each other.)

Student responses
Section 70856
(A) : 0 students
(B) : 0 students
(C) : 0 students
(D) : 11 students

Success level: 100%
Discrimination index (Aubrecht & Aubrecht, 1983): 0

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Physics quiz question: reflection phase shifts (Spring semester 2010).