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lecture 18 - sound waves

# lecture 18 - sound waves - Announcements Prayer...

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Announcements 2/16/11 Prayer Exams… hopefully graded by Friday Extra time on Lab 3:  now due Tues Feb 22. Monday Feb 21 is President’s Day holiday. Tues Feb 22 is a virtual Monday Remember in HW 17-5b to be very careful to track  the correct peak when plotting it for t = 0.1 s and t  = 0.5 s, and when calculating the velocity of the  peak.

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Thought question A wave at frequency   traveling from a string to a rope.   ω At the junction, 80% of the power is reflected.  How much  power would be reflected if the wave was going from the  rope to the string instead? a. Much less than 80% b. A little less than 80% c. About 80% d. More than 80% e. It depends on the color of the rope. 2 1 1 2 R I A v v r v v A - = = + % % 2 1 2 2 T I A v t v v A = = + % % 2 R r = 1 T R = -
Demo Reflection at a boundary

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Dispersion Summary A dispersive  medium: velocity is different for  different frequencies Any wave that isn’t 100% sinusoidal contains  multiple frequencies. To localize a wave in space or time, you need lots  of frequencies… really an infinite number of  frequencies spaced infinitely closely together.
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