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FinalExamSolution - PHYSICS 9B FINAL EXAM December 8 2010 I...

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Unformatted text preview: PHYSICS 9B FINAL EXAM December 8, 2010 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) A water flows through a horizontal pipe of the shape as shown. Where is the water pressure larger? A. From the left B. From the right C. In the middle D. The same everywhere Answer B. According to Bernoulli’s equation p+ ρ v 2 /2+ ρ gh=const., hence the larger the speed the smaller the pressure (at a constant height). It is also clear that since the water slows down while flowing from the left to the right, it is the force due to pressure difference which is responsible for it. Problem 2. (2 points) A sound source and a listener are both at rest but a strong wind is blowing from the source towards the listener. Is there a Doppler effect? A. Yes B. No. Solution . Let’s consider a coordinate system associated with the wind. Then, both the source and the listener move with the same velocity in one direction. Hence, there is no Doppler effect, answer B. Problem 3. (2 points) When light travels from medium “X” to medium “Y” as shown in the figure: A. both the speed and the wavelength increase B. both the speed and the frequency increase C. both the wavelength and the frequency are unchanged D. both the speed and the wavelength decrease E. both the speed and the frequency decrease Solution. Since the light bends away from normal, the refraction index n X of medium X is larger than refraction index n Y of medium Y. Hence speed and wavelength increase (frequency f=v/ λ stays the same), answer A. Problem 4. (2 points) If light is reflected from a window, the reflected light A. has no phase shift with respect to incident light B. has a phase shift equal to π /2 with respect incident light C. has a phase shift equal to π with respect incident light D. has a phase shift equal to 3 π /2 with respect incident light Solution. Since window glass has its refraction index larger than the refraction index of the air, the light will reflect with phase shift equal to π . Answer C. X Y Problem 5. (2 points) When an object with a hole undergoes thermal expansion, the hole A. Will expand B. Will collapse C. Will not change in size Answer A. The easiest way to understand it is to first consider the object with no hole. It will expand uniformly....
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FinalExamSolution - PHYSICS 9B FINAL EXAM December 8 2010 I...

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