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p2f10_lec08_sound_waves_resonance_and_interference

# p2f10_lec08_sound_waves_resonance_and_interference -...

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1 Sound and Electromagnetic waves Wave superposition and interference Physics 1200 Lecture 8

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2 Announcements Please bring laptops to class Oct 22/23. Please fg-lite onto your laptop for use in class.
3 Lecture Demonstrations Classroom speakers for sound test Speaker and fur for longitudinal sound waves Latex string for wave reflections and resonance Cardboard organ pipe for resonance and speed of sound (+ LoggerPro) Aluminum rod for speed of sound in metal Flame tube for resonance

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Waves on a string - summary 2 2 ( ) sin( ) ( ) The disturbance moves along the string at speed but no piece of the string travels with the wave. Each piece of string moves transversely. Restoring force: m transverse y t y kx t d y F ma t m dt τ μ ϖ = - = = = 2 sin( ) m my kx t ϖ ϖ - -
Sound Waves In sound waves a small volume of material is displaced by pressure and the restoring force is due to the change in volume of the material and the response of the material to compression (the bulk mo p / dulus). Bulk modulus: By analogy to the string we can deduce: where =mass density p B V V B v ρ ρ = =

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Sound Waves s ( x , t ) = s m cos (k (x ν t) + φ ) (displacement) – displacement of air from equilibrium position p ( x , t ) = p m sin ( k(x ν t) + φ ) (pressure) – change in pressure due to wave – out of phase with s Positive  p is a compression of the air. Negative  p is an expansion of the air. Speed in air: v = 343 m/s
Sound Facts Speed in air at STP: v = 343 m/s Sound travels more slowly as temperature is decreased (331 m/s at 00 C). The maximum tolerable pressure amplitude ~ 28 Pa. (1 atm=105Pa) Maximum displacement amplitude: ~ 10-5 m. The musician’s “pitch” is related to the scientist’s “frequency”. Higher frequency=higher pitch

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What’s the highest sound frequency that you think you can hear? A) 50 Hz B) 150 Hz C) 1500 Hz D) 15000 Hz E) Infinity, I am a maverick. iClicker Question 8.01
The iClicker Hearing and Speaker Test Please respond as the pitch is varied. A= I hear it. B= I don’t hear it.

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p2f10_lec08_sound_waves_resonance_and_interference -...

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