p2020chap08 - PHYS-2020 General Physics II Course Lecture...

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Unformatted text preview: PHYS-2020: General Physics II Course Lecture Notes Section VIII Dr. Donald G. Luttermoser East Tennessee State University Edition 3.3 Abstract These class notes are designed for use of the instructor and students of the course PHYS-2020: General Physics II taught by Dr. Donald Luttermoser at East Tennessee State University. These notes make reference to the College Physics, 9th Edition (2012) textbook by Serway and Vuille. VIII. Sound A. Characteristics of Sound Waves. 1. Sound waves are compression and rarefactions is some medium ( e.g. , air or water) and propagate like longitudinal waves. 2. Categories of Sound Waves: a) Audible waves are longitudinal waves which the human ear is sensitive = ⇒ 20 – 20,000 Hz. b) Infrasonic waves have f < 20 Hz. c) Ultrasonic waves have f > 20 , 000 Hz = 20 kHz. 3. The method of transforming electrical energy to mechanical en- ergy in crystals is called the piezoelectric effect . 4. The speed of sound in a medium follows v = radicaltp radicalvertex radicalvertex radicalbt elastic property inertial property . (VIII-1) a) For liquid or gas, elastic properties are described by the Bulk Modulus (from General Physics I ): B ≡ - Δ P Δ V/V , (VIII-2) where P is pressure (in Pa) and V is volume (Δ V and V must have the same units). b) Inertial properties are described by the mass-density ρ , hence v = radicaltp radicalvertex radicalvertex radicalbt B ρ (for liquid or gas) . (VIII-3) VIII–1 VIII–2 PHYS-2020: General Physics II c) For a solid rod, elastic properties are given by Young’s modulus Y , or v = radicaltp radicalvertex radicalvertex radicalbt Y ρ (for solid rod) . (VIII-4) d) For a gas, the Bulk Modulus is given by B = γP , where γ is constant which depends upon the composition of the gas (it is determined by the ratio of the specific heat at con- stant pressure to specific heat at constant volume , which are concepts covered in the upper-level Thermodynamics course that we offer). As such, the speed of sound in a gas depends the pressure and density of the gas following v = radicaltp radicalvertex radicalvertex radicalbt γP ρ . (VIII-5) i) If we make use of the ideal gas law, P = ρk B T/ ( μm H ), we can write the speed of sound in terms of tem- perature T (measured in K): v = radicaltp radicalvertex radicalvertex radicalbt γρk B T μm H ρ = radicaltp radicalvertex radicalvertex radicalbt γk B T μm H . (VIII-6) ii) We can determine sound speeds at any tempera- ture if we can determine it at some reference tem- perature T ◦ by setting up a ratio using Eq. (VIII-6): v v ◦ = radicaltp radicalvertex radicalvertex radicalvertex radicalbt γk B T/ ( μm H ) γk B T ◦ / ( μm H ) = radicaltp radicalvertex radicalvertex radicalbt T T ◦ ....
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This note was uploaded on 03/21/2012 for the course PHY 2020 taught by Professor Staff during the Fall '08 term at University of Florida.

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p2020chap08 - PHYS-2020 General Physics II Course Lecture...

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