F11Physics1CLec14A

F11Physics1CLec14A - Physics 1C Lecture 14A "The finest...

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Physics 1C Lecture 14A "The finest words in the world are only vain sounds if you cannot understand them." --Anatole France
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Announcements Today cover: Wave Interference Standing Waves Beat frequencies
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Sound Interference Example Two loudspeakers are 2.0m apart and are driven by the same oscillator. Both speakers emit 700Hz sound waves into a room where the speed of sound is 341m/s. A listener stands 5.0m in front of the speakers and 2.0m to one side of the center. Does the listener experience constructive interference, destructive interference, or neither at this location?
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Sound Interference Answer We need to calculate the path length difference, Δ r . So we should calculate the difference between r 2 and r 1 . Speaker 1 5m 1m r 1 Speaker 2 5m 3m r 2
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Sound Interference The path length difference at this location is a half-integer wavelength, so we should have destructive interference . <- Rounding to two places Comparing this to the path length difference gives: Answer Next, we should see how many multiples of the wavelength this path length difference is (integer, half- integer, or neither). So we should calculate the wavelength of this sound wave. 1.5
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Standing Waves in Strings For a string fixed at both ends, the longest standing wave we can achieve is: l = 2L The frequency for this standing wave is known as the fundamental frequency or the first harmonic . The length, L , of the string is equal to one-half the wavelength. We label standing waves by the number of anti-nodes, so this wave is n = 1 .
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The next longest wavelength that we can achieve on this string is n = 2 . Here,
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This note was uploaded on 12/11/2011 for the course PHYS 1C taught by Professor Smith during the Fall '07 term at UCSD.

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F11Physics1CLec14A - Physics 1C Lecture 14A "The finest...

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