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Unformatted text preview: a trough? (A) 8 s
(B) 4 s
(C) 2 s
(D) 1 s Page 2 of 7 UIC PHYSICS 105 Spring 2012 Practice Exam 3 MC6: The frequency of a siren is 20% more when the fire truck is approaching you than after
passing you as you stand on the sidewalk. The speed of the fire truck is:
(A) 48 m/s
(B) 38 m/s
(C) 28 m/s
(D) 18 m/s
MC7: An unknown film floating on water (n=1.33) appears dark at its edges where the film's thickness
is approaching zero. As you know, this is due to thin film interference, but the thickness of the film is
almost zero; so there must be a single phase shift in one of the two reflections. You conclude that the
index of refraction of the unknown film must be:
(A) greater than 1.33
(B) equal 1.33
(C) less than 1.33
(D) None of these can be predicted for sure.
MC8: You are playing in the lab with your laser and your diffraction grating. If you change your red
(650 nm) laser to a green (500 nm) laser, what happens to the spacing of the maxima projected from
the diffraction grating?
(A) The spacing gets smaller
(B) The spacing remains the same
(C) The spacing gets larger
(D) None of these can be predi...
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- Spring '12