Assignment_7_08

Assignment_7_08 - Physics 214 Assignment 7 Concepts Beats...

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Physics 214 Assignment 7 Concepts: Beats Energy in waves Power and Intensity Electromagnetic waves Reading: AG Notes on Mechanical Waves; Y&F, Vol. 2, Chapter 32 Assignment: Due in lecture on Thursday, March 13. Please turn in this sheet stapled to the top of your work. Physics Problems: 1. Suppose that you have two loudspeakers side by side, broadcasting sound in the same direction. You drive one to produce a sound wave s 1 (x,t) = s m cos (k 1 x - ω 1 t) and the other to produce a sound wave s 2 (x,t) = s m cos (k 2 x - ω 2 t). Let's assume that the difference in frequency ω 1 - ω 2 is 0.1 times the average of ω 1 and ω 2 . (a) Sketch the resulting displacement wave s(x,t) = s 1 (x,t) + s 2 (x,t) versus time at x=0, for two period of the overall waveform. (b) Sketch the displacement wave s(x,t) = s 1 (x,t) + s 2 (x,t) versus position at t=0 for two spatial periods of the overall waveform. (c) Think about your answer to (b). If you start at the speakers and walk away from them in the +x direction, would you expect to encounter positions where the sound is very quiet? Explain briefly. 2. For a harmonic traveling wave on a string, y(x,t) = A cos (kx - ω t), show that the kinetic and potential energies per unit length are equal at all times, i.e. u p (x,t) = u k
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This note was uploaded on 03/31/2009 for the course PHYS 214 taught by Professor Thorne during the Spring '08 term at Cornell.

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Assignment_7_08 - Physics 214 Assignment 7 Concepts Beats...

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