1 Fall 2004 Physics 3 Tu-Th Section Claudio Campagnari Lecture 3: 30 Sep. 2004 Web page:

Slides:



Advertisements
Similar presentations
10/31/2013PHY 113 C Fall Lecture 181 PHY 113 C General Physics I 11 AM -12:15 PM TR Olin 101 Plan for Lecture 18: Chapter 17 – Sound Waves, Doppler.
Advertisements

Chapter 12 SOUND.
Faculty of Computers and Information Fayoum University 
Dr. Jie ZouPHY Chapter 17 Sound Waves. Dr. Jie ZouPHY Outline Sound waves in general Speed of sound waves Periodic sound waves Displacement.
Chapter 14 Sound.
Sound Waves. Producing a Sound Wave Sound waves are longitudinal waves traveling through a medium A tuning fork can be used as an example of producing.
Sound Chapter 15.
Phys 250 Ch15 p1 Chapter 15: Waves and Sound Example: pulse on a string speed of pulse = wave speed = v depends upon tension T and inertia (mass per length.
Happyphysics.com Physics Lecture Resources Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com.
Chapter 17 Sound Waves. Introduction to Sound Waves Waves can move through three-dimensional bulk media. Sound waves are longitudinal waves. They travel.
Chapter 17 - Waves II In this chapter we will study sound waves and concentrate on the following topics: Speed of sound waves Relation between displacement.
Chapter 19 Sound Waves Molecules obey SHM s(x,t)=smcos(kx-t)
Sound Physics 202 Professor Lee Carkner Lecture 9.
Sound Physics 202 Professor Lee Carkner Lecture 8.
Cutnell/Johnson Physics 8th edition Reading Quiz Questions
1 Fall 2004 Physics 3 Tu-Th Section Claudio Campagnari Lecture 2: 28 Sep Web page:
1 Sinusoidal Waves The waves produced in SHM are sinusoidal, i.e., they can be described by a sine or cosine function with appropriate amplitude, frequency,
1 Fall 2004 Physics 3 Tu-Th Section Claudio Campagnari Web page:
Phy 202: General Physics II Ch 16: Waves & Sound Lecture Notes.
1 Fall 2004 Physics 3 Tu-Th Section Claudio Campagnari Lecture 4: 5 Oct Web page:
Chapter 16 Sound and Hearing.
Phy 212: General Physics II
PHYS 218 sec Review Chap. 15 Mechanical Waves.
Chapters 16 – 18 Waves.
Waves Traveling Waves –Types –Classification –Harmonic Waves –Definitions –Direction of Travel Speed of Waves Energy of a Wave.
James T. Shipman Jerry D. Wilson Charles A. Higgins, Jr. Waves and Sound Chapter 6.
Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapters 11 – 12 Waves and Sound.
Waves and Sound Ch
Mechanics & Mechanical wave phenomena
Chapter 16 Outline Sound and Hearing Sound waves Pressure fluctuations Speed of sound General fluid Ideal gas Sound intensity Standing waves Normal modes.
1 Mechanical Waves Ch Waves A wave is a disturbance in a medium which carries energy from one point to another without the transport of matter.
Mechanical Waves Ch Waves A wave is a disturbance in a medium which carries energy from one point to another without the transport of matter.
Sound Waves Sound waves are divided into three categories that cover different frequency ranges Audible waves lie within the range of sensitivity of the.
Chapter 13 - Sound 13.1 Sound Waves.
Chapter 17: [Sound] Waves-(II)
Sound Waves. Review Do you remember anything about _______? Transverse waves Longitudinal waves Mechanical waves Electromagnetic waves.
1 Characteristics of Sound Waves. 2 Transverse and Longitudinal Waves Classification of waves is according to the direction of propagation. In transverse.
Chapter 14 Waves and Sound
Physics 207: Lecture 21, Pg 1 Physics 207, Lecture 21, Nov. 15 l Agenda: l Agenda: Chapter 16, Finish, Chapter 17, Sound  Traveling Waves  Reflection.
Chapter 17 Sound Waves: part one. Introduction to Sound Waves Sound waves are longitudinal waves They travel through any material medium The speed of.
Chapter 13 Mechanical Waves. Types of Waves There are two main types of waves Mechanical waves Some physical medium is being disturbed The wave is the.
Wave - II.
Chapter 14 Sound. Sound waves Sound – longitudinal waves in a substance (air, water, metal, etc.) with frequencies detectable by human ears (between ~
CH 14 Sections (3-4-10) Sound Wave. Sound is a wave (sound wave) Sound waves are longitudinal waves: longitudinal wave the particle displacement is parallel.
Types of Traveling Waves
Introduction to Waves and Sound Chapters 14 and 15.
Copyright © 2009 Pearson Education, Inc. Lecture 1 – Waves & Sound b) Wave Motion & Properties.
Chapter 16 Waves and Sound The Nature of Waves 1.A wave is a traveling disturbance. 2.A wave carries energy from place to place.
Physics 101: Lecture 33 Sound
R. Field 4/16/2013 University of Florida PHY 2053Page 1 Sound: Propagation Speed of Sound: The speed of any mechanical wave depends on both the inertial.
Sound Waves Vibration of a tuning fork
Chapters 16, 17 Waves.
Slide 17-1 Lecture Outline Chapter 17 Waves in Two and Three Dimensions © 2015 Pearson Education, Inc.
Chapter 11 Vibrations and Waves.
1 Linear Wave Equation The maximum values of the transverse speed and transverse acceleration are v y, max =  A a y, max =  2 A The transverse speed.
Honors Physics Chapter 14
Chapter 13 Wave Motion.
Chapter 15: Wave Motion 15-2 Types of Waves: Transverse and Longitudinal 15-3 Energy Transported by Waves 15-4 Mathematical Representation of a Traveling.
Chapter 12: Sound and Light. Goals/Objectives  After completing the lesson, students will be able to...  Recognize what factors affect the speed of.
Raymond A. Serway Chris Vuille Chapter Fourteen Sound.
Wave Motion Types of mechanical waves  Mechanical waves are disturbances that travel through some material or substance called medium for the waves. travel.
Chapter 17 Sound Waves 17.1 Pressure variation in Sound Waves 17.2 speed of Sound Waves 17.3 Intensity of Periodic Sound Waves 17.4 The Doppler Effect.
Chapter The Nature of Waves 1.A wave is a traveling disturbance. 2.A wave carries energy from place to place.
Physics 1 What is a wave? A wave is: an energy-transferring disturbance moves through a material medium or a vacuum.
Chapter 16 Sound and Hearing.
Chapter 17 Sound Waves.
Lecture 11 WAVE.
Physics 7E Prof. D. Casper.
Waves What is a wave?.
Reflection Superposition Interference
Presentation transcript:

1 Fall 2004 Physics 3 Tu-Th Section Claudio Campagnari Lecture 3: 30 Sep Web page:

2 Sound Sound = longitudinal wave in a medium. The medium can be anything: –a gas, e.g., air –a liquid, e.g., water –even a solid, e.g., the walls The human hear is "sensitive" to frequency range ~ 20-20,000 Hz –"audible range" –higher frequency: "ultrasounds" –lower frequency: "infrasound"

3 How do we describe such a wave? e.g., sinusoidal wave, traveling to the right –idealized one dimensional transmission, like a sound wave within a pipe. Mathematically, just like transverse wave on string: y(x,t) = A cos(kx-  t) But the meaning of this equation is quite different for a wave on a string and a sound wave!!

4 y=A cos(kx-  t) "x" = the direction of propagation of the wave "y(x,t)" for string is the displacement at time t of the piece of string at coordinate x perpendicular to the direction of propagation. "y(x,t)" for sound is the displacement at time t of a piece of fluid at coordinate x parallel to the direction of propagation. "A" is the amplitude, i.e., the maximum value of displacement. ccc x x y y A y A

5 It is more convenient to describe a sound wave not in term of the displacement of the particles in the fluid, but rather in terms of the pressure in the fluid. Displacement and pressure are clearly related:

6 In a sound wave the pressure fluctuates around the equilibrium value. –For air, this would normally be the atmospheric pressure. –p absolute (x,t) = p atmospheric + p(x,t) Let's relate the fluctuating pressure p(x,t) to the displacement defined before.

7

8  V = change in volume of cylinder:  V = S ¢ (y 2 -y 1 ) = S ¢ [ y(x+  x,t) - y(x,t) ] Original volume: V = S ¢  x Fractional volume change:

9 Now make  x infinitesimally small –Take limit  x  0 –  V becomes dV Bulk modulus: B (chapter 11)

10 This is the equation that relates the displacement of the particles in the fluid (y) to the fluctuation in pressure (p). They are related through the bulk modulus (B) Fractional volume change Applied pressure Bulk modulus Definition of bulk modulus:

11 Sinusoidal wave This then gives Displacement (y) and pressure (p) oscillations are 90 o out of phase

12 Example "Typical" sinusoidal sound wave, maximum pressure fluctuation 3 £ Pa. –Compare p atmospheric = 1 £ 10 5 Pa Find maximum displacement at f=1 kHz given that B= Pa, v=344 m/sec 1 Pa = 1 N/m 2

13 We have p max (= 3 £ Pa) and B (= 1.4 £ 10 5 Pa) But what about k? We have f and v  = v/f And k = 2  /   k = 2  /(v/f) = 2  f/v

14 Now it is just a matter of plugging in numbers:

15 Aside: Bulk Modulus, Ideal Gas Careful: P here is not the pressure, but its deviation from equilibrium, e.g., the additional pressure that is applied to a volume of gas originally at atmospheric pressure. Better notation P  dP

16 For adiabatic process, ideal gas: Heat capacities at constant P or V  ~ 1.7 monoatomic molecules (He, Ar,..)  ~ 1.4 diatomic molecules (O 2, N 2,..)  ~ 1.3 polyatomic molecules (CO 2,..) Differentiate w.r.t. V: But bulk modulus

17 Note: the bulk modulus increases with pressure. If we increase the pressure of a gas, it becomes harder to compress it further, i.e. the bulk modulus increases (makes intuitive sense)

18 Speed of sound - At t=0 push the piston in with constant v y This triggers wave motion in fluid - At time t, piston has moved distance v y t - If v is the speed of propagation of the wave, i.e. the speed of sound, fluid particles up to distance vt are in motion - Mass of fluid in motion M=  Avt - Speed of fluid in motion is v y - Momentum of fluid in motion is Mv y =  Avtv y -  P is the change in pressure in the region where fluid is moving - V = Avt and  V = -Av y t

19 Net force on fluid is F = (p+  p) ¢ A – p ¢ A =  p ¢ A This force has been applied for time t: Impulse = change in momentum Initial momentum = 0 Final momentum =  Avtv y

20 Speed of sound: Speed of waves on a string: B and F quantify the restoring "force" to equilibrium.  and  are a measure of the "inertia" of the system.

21 Speed of sound: Bulk modulus: One mole of ideal gas: R = gas constant R ~ 8.3 J/mol K Since  V = mass per mole = M:

22 For air: –  = 1.4 –M = g/mol At T = 20 o C = 293 o K: A function of the gas and the temperature He: 1000 m/sec H 2 : 1330 m/sec

23 Intensity The wave carries energy The intensity is the time average of the power carried by the wave crossing unit area. Intensity is measured in W/m 2

24 Intensity (cont.) Sinusoidal sound wave: Power = Force £ velocity Intensity = /Area = /Area = Particle velocity NOT wave velocity

25 Intensity (cont.) Now use  = vk and v 2 =B/  : ½ Or in terms of p max = BkA: And using v 2 =B/  :

26 Decibel A more convenient sound intensity scale –more convenient than W/m 2. The sound intensity level  is defined as Where I 0 = W/m 2 –Approximate hearing threshold at 1 kHz It's a log scale –A change of 10 dB corresponds to a factor of 10

27

28 Example Consider a sound source. Consider two listeners, one of which twice as far away as the other one. What is the difference (in decibel) in the sound intensity perceived by the two listeners?

29 To answer the question we need to know something about the directionality of the emitted sound. Assume that the sound is emitted uniformly in all directions.

30 How does the intensity change with r (distance from the source)? The key principle to apply is conservation of energy. The total energy per unit time crossing a spherical surface at r 1 must equal the total energy crossing a spherical surface at r 2 Surface area of sphere of radius r: 4  r 2. Intensity = Energy/unit time/unit area. 4  r 1 2 I 1 = 4  r 2 2 I 2.

31 The original question was: change in decibels when second "listener" is twice as far away as first one. r 2 = 2r 1 I 1 /I 2 = 4 Definition of decibel :

32 Standing sound waves Recall standing waves on a string Nodes A standing wave on a string occurs when we have interference between wave and its reflection. The reflection occurs when the medium changes, e.g., at the string support.

33 We can have sound standing waves too. For example, in a pipe. Two types of boundary conditions: 1.Open pipe 2.Closed pipe In an closed pipe the boundary condition is that the displacement is zero at the end  Because the fluid is constrained by the wall, it can't move! In an open pipe the boundary condition is that the pressure fluctuation is zero at the end  Because the pressure is the same as outside the pipe (atmospheric)

34 Remember: Displacement and pressure are out of phase by 90 o. When the displacement is 0, the pressure is ± p max. When the pressure is 0, the displacement is ± y max. So the nodes of the pressure and displacement waves are at different positions –It is still the same wave, just two different ways to describe it mathematically!!

35 More jargon: nodes and antinodes In a sound wave the pressure nodes are the displacement antinodes and viceversa Nodes Antinodes

36 Example A directional loudspeaker bounces a sinusoidal sound wave of the wall. At what distance from the wall can you stand and hear no sound at all? A key thing to realize is that the ear is sensitive to pressure fluctuations Want to be at pressure node The wall is a displacement node  pressure antinode (displacement picture here)