2054Lecture3 - Sound Waves Sound Topics of Discussion...

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Unformatted text preview: Sound Waves Sound Topics of Discussion Topics Sound Waves Sound Waves in an Air Column Sound Intensity & the Decibel The Doppler Effect Sound Waves Sound Sound waves are longitudinal waves. The speed of sound depends on the material The through which the wave travels. through Let γ be the ratio of the specific heat at Let constant pressure to constant volume of an ideal gas. Then, for an ideal gas of mass m held at a temperature T, the speed of the the wave v is given by v= kγ T m where k=1.380×10-23J/K is Boltzmann’s where k=1.380 constant. Standing Waves in an Air Column Standing If both ends of an air column are open then If the nth-harmonic wave is given by fn=nv/2L=nf1, wave where n=2,3,…and f1=v/2L. n=2,3,…and If one end of an air column is open then the If nth-harmonic wave is given by fn=nv/4L=nf1, wave where n=2,3,… and f1=v/4L. n=2,3,… A node (An anti-node) must exist at the node closed (open) end of the air column since the motion is restricted (unrestricted). motion Sound Intensity & the Decibel Sound Sound intensity is given by I=P/A, where P Sound I=P/A where is the sound power and A is the area perpendicular to the motion of the sound wave. The decibel (dB) iis a measurement of s The decibel sound intensity between two sources of intensity I and I0, and is given by and and β=(10dB)log(I/I0). The Doppler Effect The Let the speed of sound be v. Let fS be the Let Let frequency of the source S traveling at a speed vS. Then the frequency of a source Then as heard by a moving observer O with speed vO is given by vO 1± v fO = f S 1 ± vS v Conventions for the Doppler Effect Conventions In the numerator, the + sign indicates In that the observer moves towards the source and the – sign indicates that the observer moves away from the source. observer In the denominator, the + sign indicates In that the source moves away the observer and the – sign indicates that the source moves towards the observer. the ...
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