ef152-lec-4-2 - Module 4, Lecture 2: Beats, Doppler, Sonic...

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EF 152 Spring, 2009 Lecture 4-2 1 Module 4, Lecture 2: Beats, Doppler, Sonic Boom Beats: Beats occur when two waves of almost the same frequency are superimposed. () ( ) t kx A t x z ω = sin , Wave equation: At a fixed point in space: () ( ) t f A t A D i i i ω 2 sin sin = = Add the two waves together, and use some trig identities: + = + t f f t f f A D D 2 2 sin 2 2 cos 2 2 1 2 1 2 π EF 152 Spring, 2009 Lecture 4-2 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 0 5 10 15 20 25 30 35 40 Time (t) Amplitude D1 D2 D1+D2 Envelope f 1 = 1.05 Hz f 2 = 1.00 Hz Hearing beat frequency EF 152 Spring, 2009 Lecture 4-2 3 Example: Tuning Fork Given : A tuning fork produces a steady 400 Hz tone. When struck and held near a vibrating guitar string, twenty beats are counted in 5 seconds. Required : Possible frequencies produced by guitar string. A. 380 Hz, 420 Hz B. 396 Hz, 404 Hz C. 395 Hz, 405 Hz D. 400 Hz EF 152 Spring, 2009 Lecture 4-2 4 Doppler Effect
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This note was uploaded on 04/07/2009 for the course EF 152 taught by Professor Ab during the Spring '08 term at University of Tennessee.

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ef152-lec-4-2 - Module 4, Lecture 2: Beats, Doppler, Sonic...

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