2. Waves and Sound An Introduction to Waves and Wave Properties

3. Waves and Sound Exam Week Also Beginning Electrostatics… 02/22-26/10

4. Monday Objective: Find the wavelength for sound waves using resonance of closed pipes Objective: Find the wavelength for sound waves using resonance of closed pipes Go over Friday’s Circular Motion Exam Go over Friday’s Circular Motion Exam FRQ Practice: End of waves ppt. notes #1 FRQ Practice: End of waves ppt. notes #1 “Organ Pipes” Lab – closed pipe resonance “Organ Pipes” Lab – closed pipe resonance HW: Due tomorrow: HW Packets – “Waves and Sound”, and “Superposition and Interference” HW: Due tomorrow: HW Packets – “Waves and Sound”, and “Superposition and Interference” FR Quiz Wednesday on Sound Waves FR Quiz Wednesday on Sound Waves FR Quiz Thursday on Phy Ops FR Quiz Thursday on Phy Ops Extra Session Thurs after school – Waves and Sound Exam Review Extra Session Thurs after school – Waves and Sound Exam Review Waves and Sound Exam on Friday Waves and Sound Exam on Friday

5. BW’s

6. Tuesday Objective: TSWBAT describe the wave nature of light as it relates to diffraction and interference (Physical Optics, “Phy Ops”) Objective: TSWBAT describe the wave nature of light as it relates to diffraction and interference (Physical Optics, “Phy Ops”) Check HW Packets – “Waves and Sound”, and “Superposition and Interference” Check HW Packets – “Waves and Sound”, and “Superposition and Interference” Give and go over answers Give and go over answers Phy Ops FR Practice Problem – Waves PPT. notes Practice #1 Phy Ops FR Practice Problem – Waves PPT. notes Practice #1 HW Packet – Phy Ops (Due tomorrow) HW Packet – Phy Ops (Due tomorrow) FR Quiz tomorrow on Sound Waves FR Quiz tomorrow on Sound Waves FR Quiz Thursday on Phy Ops FR Quiz Thursday on Phy Ops Extra Session Thurs after school – Waves and Sound Exam Review Extra Session Thurs after school – Waves and Sound Exam Review Waves and Sound Exam on Friday Waves and Sound Exam on Friday

7. Wednesday OBJECTIVE: TSWBAT define charge and polarization OBJECTIVE: TSWBAT define charge and polarization Check Phy Ops HW packet Check Phy Ops HW packet Give and go over answers Give and go over answers FR Quiz on Sound Waves – Partners allowed FR Quiz on Sound Waves – Partners allowed FR Quiz tomorrow on Phy Ops FR Quiz tomorrow on Phy Ops If time: Begin Electrostatics! – Charge and Polarization – Demos: Balloon and electroscope If time: Begin Electrostatics! – Charge and Polarization – Demos: Balloon and electroscope Extra Session tomorrow after school – Waves and Sound Exam Review Extra Session tomorrow after school – Waves and Sound Exam Review Waves and Sound Exam on Friday Waves and Sound Exam on Friday

8. Thursday Objective: Define Coulomb’s Law and use it to find electric forces between charges Objective: Define Coulomb’s Law and use it to find electric forces between charges Go over Sound Waves FR Quiz from yesterday Go over Sound Waves FR Quiz from yesterday FR Quiz – Phy Ops – Partners allowed FR Quiz – Phy Ops – Partners allowed Red pen grade FR Quiz Red pen grade FR Quiz Electrostatics: Coulomb’s Law, E. Force, and E. Fields PPT. notes Electrostatics: Coulomb’s Law, E. Force, and E. Fields PPT. notes HW: Complete the Electrostatics PPt. notes over the weekend (Download the ppt. tonight…) HW: Complete the Electrostatics PPt. notes over the weekend (Download the ppt. tonight…) Waves and Sound Exam tomorrow Waves and Sound Exam tomorrow Extra Session today after school Extra Session today after school

9. Friday Take Waves and Sound Exam Take Waves and Sound Exam HW: Complete Electrostatics Notes over the weekend (download the powerpoint file on our class website) HW: Complete Electrostatics Notes over the weekend (download the powerpoint file on our class website)

10. Mechanical Wave A mechanical wave is a disturbance which propagates through a medium with little or no net displacement of the particles of the medium. Wave “Pulse” Water Waves Animation courtesy of Dr. Dan Russell, Kettering University People Wave

11. Parts of a Wave 3 -3 246 x(m) y(m) A: amplitude : wavelength crest trough equilibrium

12. Speed of a wave  The speed of a wave is the distance traveled by a given point on the wave (such as a crest) in a given interval of time.  v = d/t d: distance (m) d: distance (m) t: time (s) t: time (s)  v = ƒ v : speed (m /s) v : speed (m /s) : wavelength (m) : wavelength (m) ƒ : frequency (s –1, Hz) ƒ : frequency (s –1, Hz)

13. Period of a wave  T = 1/ƒ T : period (s) T : period (s) ƒ : frequency (s -1, Hz) ƒ : frequency (s -1, Hz)

14. Wave Types A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction which the wave moves. Example: Waves on a String A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction which the wave moves. These are also called compression waves. Example: sound http://einstein.byu.edu/~masong/HTMstuff/WaveTrans.html

15. Wave types: transverse

16. Wave types: longitudinal

17. Longitudinal vs Transverse

18. Other Wave Types  Earthquakes: combination  Ocean waves: surface  Light: electromagnetic

19. Reflection of waves Occurs when a wave strikes a medium boundary and “bounces back” into original medium.Occurs when a wave strikes a medium boundary and “bounces back” into original medium. Completely reflected waves have the same energy and speed as original wave.Completely reflected waves have the same energy and speed as original wave.

20. Reflection Types  Fixed-end reflection: The wave reflects with inverted phase.  Open-end reflection: The wave reflects with the same phase Animation courtesy of Dr. Dan Russell, Kettering University

21. Refraction of waves Transmission of wave from one medium to another.Transmission of wave from one medium to another. Refracted waves may change speed and wavelength.Refracted waves may change speed and wavelength. Refraction is almost always accompanied by some reflection.Refraction is almost always accompanied by some reflection. Refracted waves do not change frequency.Refracted waves do not change frequency. Animation courtesy of Dr. Dan Russell, Kettering University

22. Slinky Demos  Demonstrate a transverse wave pulse.  Demonstrate a longitudinal wave pulse.  Demonstrate fixed-end reflection of transverse pulse.  Demonstrate open-end reflection of transverse pulse.

23. Sound Waves

24. Sound is a longitudinal wave  Sound travels through the air at approximately 340 m/s.  It travels through other media as well, often much faster than that!  Sound waves are started by vibration of some other material, which starts the air moving. Animation courtesy of Dr. Dan Russell, Kettering University

25. Hearing Sounds  We hear a sound as “high” or “low” depending on its frequency or wavelength. Sounds with short wavelengths and high frequencies sound high-pitched to our ears, and sounds with long wavelengths and low frequencies sound low-pitched. The range of human hearing is from about 20 Hz to about 20,000 Hz.  The amplitude of a sound’s vibration is interpreted as its loudness. We measure the loudness (also called sound intensity) on the decibel scale, which is logarithmic. © Tom Henderson, 1996-2004

26. Doppler Effect The Doppler Effect is the raising or lowering of the perceived pitch of a sound based on the relative motion of observer and source of the sound. When a car blowing its horn races toward you, the sound of its horn appears higher in pitch, since the wavelength has been effectively shortened by the motion of the car relative to you. The opposite happens when the car races away.

27. Doppler Effect Stationary source Moving source Supersonic source Animations courtesy of Dr. Dan Russell, Kettering University http://www.kettering.edu/~drussell/Demos/doppler/mach1.mpg

28. Pure Sounds  Sounds are longitudinal waves, but if we graph them right, we can make them look like transverse waves.  When we graph the air motion involved in a pure sound tone versus position, we get what looks like a sine or cosine function.  A tuning fork produces a relatively pure tone. So does a human whistle.

29. Graphing a Sound Wave

30. Complex Sounds  Because of the phenomena of “superposition” and “interference” real world waveforms may not appear to be pure sine or cosine functions.  That is because most real world sounds are composed of multiple frequencies.  The human voice and most musical instruments produce complex sounds.

31. The Oscilloscope With the Oscilloscope we can view waveforms in the “time domain”. Pure tones will resemble sine or cosine functions, and complex tones will show other repeating patterns that are formed from multiple sine and cosine functions added together.

32. The Fourier Transform Shows waveforms in the “frequency domain”. A mathematical technique called the Fourier Transform will separate a complex waveform into its component frequencies.

33. Superposition and Interference

34. Principle of Superposition  When two or more waves pass a particular point in a medium simultaneously, the resulting displacement at that point in the medium is the sum of the displacements due to each individual wave.  The waves interfere with each other.

35. Types of interference.  If the waves are “in phase”, that is crests and troughs are aligned, the amplitude is increased. This is called constructive interference.  If the waves are “out of phase”, that is crests and troughs are completely misaligned, the amplitude is decreased and can even be zero. This is called destructive interference.

36. Interference  Let’s watch some exciting Physics Movies!

37. Constructive Interference crests aligned with crest waves are “in phase”

38. Constructive Interference

39. Destructive Interference crests aligned with troughs waves are “out of phase”

40. Destructive Interference

41. Sample Problem: Draw the waveform from its two components.

43. Standing Waves

44. Standing Wave  A standing wave is a wave which is reflected back and forth between fixed ends (of a string or pipe, for example).  Reflection may be fixed or open-ended.  Superposition of the wave upon itself results in constructive interference and an enhanced wave.

45. Fixed-end standing waves (violin string) 1 st harmonic 2 nd harmonic 3 rd harmonic http://id.mind.net/~zona/mstm/physics/waves/standingWaves/standingWaves1/StandingWaves1.html Animation available at:

46. Fixed-end standing waves (violin string) Fundamental First harmonic = 2L First Overtone Second harmonic = L Second Overtone Third harmonic = 2L/3 L

47. Open-end standing waves (organ pipes) Fundamental First harmonic = 2L First Overtone Second harmonic = L Second Overtone Third harmonic = 2L/3 L

48. Mixed standing waves (some organ pipes – Closed on one end) First harmonic = 4L Second harmonic = (4/3)L Third harmonic = (4/5)L L

49. Sample Problem  How long do you need to make string that produces a high C (512 Hz)? The speed of the waves on the string 1040 m/s. A) Draw the situation. A) Draw the situation. B) Calculate the pipe length. B) Calculate the pipe length. C) What is the wavelength and frequency of the 2 nd harmonic? C) What is the wavelength and frequency of the 2 nd harmonic?

50. Sample Problem  How long do you need to make an organ pipe whose fundamental frequency is a middle C (256 Hz)? The pipe is closed on one end, and the speed of sound in air is 340 m/s. A) Draw the situation. A) Draw the situation. B) Calculate the pipe length. B) Calculate the pipe length. C) What is the wavelength and frequency of the 2 nd harmonic? C) What is the wavelength and frequency of the 2 nd harmonic?

51. Sample Problem  How long do you need to make an organ pipe whose fundamental frequency is a middle C (256 Hz)? The pipe is open on both ends, and the speed of sound in air is 340 m/s. A) Draw the situation. A) Draw the situation. (FOLLOW the previous slide, but use the information for open-ended pipes on slide 39) B) Calculate the pipe length. B) Calculate the pipe length. C) What is the wavelength and frequency of the 2 nd harmonic? C) What is the wavelength and frequency of the 2 nd harmonic?

52. Resonance  Resonance occurs when a vibration from one oscillator occurs at a natural frequency for another oscillator.  The first oscillator will cause the second to vibrate.  Demonstration.  Another exciting physics movie.

53. Beats  “Beats” is the word physicists use to describe the characteristic loud-soft pattern that characterizes two nearly (but not exactly) matched frequencies.  Musicians call this “being out of tune”.  Let’s hear (and see) a demo of this phenomenon.

54. What word best describes this to physicists? Amplitude Answer: beats

55. What word best describes this to musicians? Amplitude Answer: bad intonation (being out of tune)

56. Organ Pipe Lab

57. organ pipe lab  Create an organ pipe that will resonate as loudly as possible with your tuning fork. a) Predict the length of your organ pipe. Draw the first harmonic for a standing wave in your pipe, and determine what fraction of a wavelength it is. Use 340 m/s as the speed of sound in air to get the wavelength from the frequency. Estimate the length of the pipe. b) Construct your organ pipe. Does it resonate loudly? c) Do “fine tuning” to adjust the length of the pipe to produce the loudest possible sound.  At the end of the period we will sound all the organ pipes at once to create a cord. The class grade depends upon the loudness of the sound. After you get a loud sound in your pipe, help somebody else!

58. Diffraction

59. Diffraction  The bending of a wave around a barrier.  Diffraction of light combined with interference of diffracted waves causes “diffraction patterns”.

60. More exciting movies  Diffraction around obstacles in a ripple tank.  Diffraction and interference in a ripple tank.

61. Double-slit or multi-slit diffraction n = dsin  n=0 n=1 n=2 n=1 

62. Diffraction of light  More exciting movies  Laser demonstrations Double slit diffraction Double slit diffraction Single slit diffraction Single slit diffraction  Determine the wavelength of the laser light from the diffraction pattern.

63. Double slit diffraction  n = d sin  n: bright band number (n = 0 for central) n: bright band number (n = 0 for central) : wavelength (m) : wavelength (m) d: space between slits (m) d: space between slits (m)  : angle defined by central band, slit, and band n  : angle defined by central band, slit, and band n  This also works for diffraction gratings.

64. Single slit diffraction  n = s sin  n: dark band number n: dark band number : wavelength (m) : wavelength (m) s: slit width (m) s: slit width (m)  : angle defined by central band, slit, and dark band n  : angle defined by central band, slit, and dark band n

65. Sample Problem  Light of wavelength 360 nm is passed through a diffraction grating that has 10,000 slits per cm. If the screen is 2.0 m from the grating, how far from the central bright band is the first order bright band?

66. Sample Problem  Light of wavelength 560 nm is passed through two slits. It is found that, on a screen 1.0 m from the slits, a bright spot is formed at x = 0, and another is formed at x = 0.03 m? What is the spacing between the slits?

67. Sample Problem  Light is passed through a single slit of width 2.1 x 10 -6 m. How far from the central bright band do the first and second order dark bands appear if the screen is 3.0 meters away from the slit?

68. Diffraction Lab

69. Diffraction Lab Using two meter sticks, a light source, a diffraction grating card, and your eye, demonstrate the diffraction of different colors of light through different angles to produce a rainbow. Then, using measurements for one color in the rainbow, and use the diffraction equation to calculate the spacing between the slits in the diffraction grating. Compare this result with the spacing you calculate from the information printed on the diffraction grating card. Turn in the following (ONE COPY PER PERSON!): - a diagram of your experimental setup - a calculation of the spacing between slits from the diffraction equation - a calculation of the spacing between slits from the information on the diffraction grating card - % difference between the two calculations. HINTS: Your textbook, page 927, has some helpful diagrams. Page 825 has the wavelengths for different colors of light. Your EYE acts as the SCREEN detecting BRIGHT SPOTS of different colors!