Lecture 37

# Lecture 37 - Introduction to Sound Waves PHY231 Lec-37...

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1 PHY231 Lec-37 Sound Waves Introduction to Sound Waves ± Sound waves are longitudinal waves ± They travel through any material medium ± The speed of the wave depends on the properties of the medium ± The mathematical description of sinusoidal sound waves is very similar to sinusoidal waves on a string Categories of Sound Waves ± The categories cover different frequency ranges ± Audible waves are within the sensitivity of the human ear ± Range is approximately 20 Hz to 20 kHz ± Infrasonic waves have frequencies below the audible range ± Ultrasonic waves have frequencies above the audible range Speed of Sound Waves ± Use a compressible gas as an example with a setup as shown at right ± Before the piston is moved, the gas has uniform density ± When the piston is suddenly moved to the right, the gas just in front of it is compressed ± Darker region in the diagram Speed of Sound Waves, cont ± When the piston comes to rest, the compression region of the gas continues to move ± This corresponds to a longitudinal pulse traveling through the tube with speed v ± The speed of the piston is not the same as the speed of the wave Speed of Sound Waves, General ± The speed of sound waves in a medium depends on the compressibility and the density of the medium ± The compressibility can sometimes be expressed in terms of the elastic modulus of the material ± The speed of all mechanical waves follows a general form: elastic property inertial property v =

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2 Speed of Sound in Liquid, Gas, and Solid Rod ± The bulk modulus (resistance to changes in volume) of the material is B ± The density of the material is ρ ± The speed of sound in that medium is ± The Young’s modulus (resistance to
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Lecture 37 - Introduction to Sound Waves PHY231 Lec-37...

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