FinalExamSolution (2)

FinalExamSolution (2) - PHYSICS 9B FINAL EXAM December 9,...

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PHYSICS 9B FINAL EXAM December 9, 2008 I certify by my signature below that I will abide by the UC Davis Code of Academic Conduct. This includes not copying from anyone else’s exam not letting any other student copy from my exam not discussing this exam with any student who has not yet taken it, nor providing any information, written or oral, that might get to a student who has not yet taken it. Anyone suspected of cheating will be automatically reported to Student Judicial Affairs. LAST NAME: FIRST NAME: STUDENT ID: (P R I N T) (P R I N T) (LAST 4 DIGITS) Signature: Problem 1. (2 points) Solution The left end of the long spring (point P) is displaced towards the right and kept there. The displacement ˙ x of point P is therefore nonzero (positive). At the instant shown, the wave pulse has not yet reached the right end of the long spring (point S), so this end has not yet been displaced. The only possible choice is D. A B C D
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Problem 2. (2 points) You see an approaching police car with the serene turned on. There is however a wind blowing in the direction opposite to the car motion. You will hear A. The sound of a lower frequency than the serene. B. The sound of the same frequency than the serene. C. The sound of a higher frequency than the serene. Solution. Assume for simplicity that the car moves to the left while wind blows to the right. Denote the car speed as v Car , the wind speed as v Wind and the sound speed in the air as v sound . Let us put ourselves into the coordinate system associated with the wind. In this coordinate system, you move to the left with the wind speed, while the car also moves to the left with the speed v Car + v Wind . A general formula for the source and listener that move in the same direction can now be applied sound listener sound wind LS S sound source sound car wind vv f ff v −− == Since numerator is larger than denominator, it is clear that f L >f S . Answer C. Problem 3. (2 points) Which of the following represents a correct reflection of a ray from a shiny silvered Christmas tree ornament? A B C Solution. As this is an example of a convex mirror, the reflected ray appears to come from the focal point. Answer A. Problem 4. (2 points) Coherent electromagnetic radiation is sent through a slit of width 0.01 mm. For which of the following wavelengths will there be no points in the diffraction pattern where the intensity is zero? A. Blue light of wavelength 500 nm B. Infrared light of wavelength 10.6 μ m C. Microwaves of wavelength 1.00 mm incident ray reflected ray incident ray reflected ray incident ray reflected ray
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D. Ultraviolet light of wavelength 50 nm. Solution. If the slit width a is less than the wavelength, there are no points at the diffraction pattern at which the intensity is zero. Both answers B and C are correct.
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This note was uploaded on 11/11/2011 for the course PHY 9B taught by Professor Cheng during the Spring '08 term at UC Davis.

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FinalExamSolution (2) - PHYSICS 9B FINAL EXAM December 9,...

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