(24) Sound Waves in an Ideal Gas

Hence the relative change in volume which is assumed

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Unformatted text preview: tive change in volume, which is assumed to be small, is (324) In the limit , this becomes (325) The pressure perturbation Equation (323), which yields associated with the volume perturbation follows from (326) or (327) giving (328) where use has been made of Equation (325). Consider a section of the gas column lying between . The - directed force acting on its left boundary is directed force acting on its right boundary is (i.e., - directed) acceleration of the section is and . The mass of this section is , whereas the - . Finally, the average longitudinal . Thus, the section's longitudinal equation of motion is written (329) In the limit , this equation reduces to (330) Finally, Equation (328) yields (331) where (332) is a constant with the dimensions of velocity, which turns out to be the sound speed in the gas. (See Section 7.1.) Figure 34: First three normal modes of an organ pipe (schematic). As an example, suppose that a standing wave is excited in a uniform organ pipe of length of the pipe lie at where , and the open end at . Let the closed end . The standing wave satisfie...
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This note was uploaded on 08/25/2013 for the course PHY 315 taught by Professor Staff during the Fall '08 term at University of Texas at Austin.

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