GEN PHYSICS A STUDIO
GEN PHYSICS A STUDIO PHY 2048C
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This 14 page Class Notes was uploaded by Garett Kovacek on Thursday September 17, 2015. The Class Notes belongs to PHY 2048C at Florida State University taught by Simon Capstick in Fall. Since its upload, it has received 31 views. For similar materials see /class/205523/phy-2048c-florida-state-university in Physics 2 at Florida State University.
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Date Created: 09/17/15
VVavcs Prof Chris Wiebe Prof Simon Capstick 7 r a 391 7 112 Why can t someone hear you scream In space 9 sf a 3 I Speed of light c 3x108 ms sound waves This IS why you see lightning before you hear the thunder Sound waves are traveling waves of air molecules compression and expansion of air molecules Sound demo Just like the linear density determines the speed of a wave in a string the speed of sound is determined by the density of the medium Speed v Bp B bulk modulus ApAVV Density of the medium p At room temperature atmospheric pressure vsound 343 ms PRS Question A traveling wave passes a point of observation At this point the time between successive crests is 02 s Which of the following is true A The wavelength is 5 m B The frequency is 5 Hz C The velocity of propagation is 5 ms D The wavelength is 02 m E There is not enough information to justify any of these statements Answer B The frequency is 5 Hz The period is 02 s so f 1T 102 s 5 Hz The frequency is the number of crests that pass by per second Waves hitting barriers What happens when a Low to high density inverted reflected wave wave hits a barrier ie another string or a wall Some of the wave is transmitted and some is reflected The wave that is reflected can be inverted low to high density or not inverted high to low density Transmitted wave is always not inverted High to low density not inverted reflected wave The Doppler Effect How do police officers measure your speed How does Doppler radar work Why does the sound change for a siren approaching you as opposed to a siren moving away from you These are all examples of the Doppler Effect the wavelength of a source changes for observers that are moving towards or away from source Doppler Effect demonstration Ahead of source wavelength decreases Behind source wavelength increases The Doppler Effect Consider a source moving with speed us and a stationary receiver The source has frequency f8 The received frequency fr is the number of wave crests passing the receiver per unit time is fr vA Let s call the time between wave crests for the moving source to be T5 The wavelength for waves in front of the source is now Af v M USTS and behind the source it 503ng is Ab vusTs So the wavelength is now 0T55 szs A vuSfs I Ill T6 Xb S thf depending upon if you are lb U 5 TS behind or In front of source M v us TS The Doppler Effect How does this affect the frequency Solve for receiver frequency Stationary receiver This equation tells you how the frequency of the stationary receiver V fr changes for a source f that is r f moving at speed us and the speed V u of sound is v s In front of wave minus sign higher freq approaching behind wave plus sign lower freq receding If the receiver is moving as well with Moving receiver and source speed ur this equation becomes gt f f Which sign to use r s Remember frequency increases for source moving towards receiver V i Mr V i us sign or receiver moving towards source sign The Doppler Effect example 1510 A car horn has a frequency of 400 Hz If the horn sounds as the car moves at 34 ms towards a stationary observer Find the wavelength of the sound heard by the observer Use 7v v us Its Source approaching minus sign 80 X 340 ms 34 ms4OO Hz 0765 m Find the frequency of the sound heard Use f f5 v Ov ug 80 f 400 Hz34O ms34034 ms 444 Hz Find 9v and f if the car is now stationary and the observer is approaching in another car at 34 ms Use x v us fs and tr v ur v us 1 8 with u8 0 So we have fr v ur v fs What sign do we use Frequency has to go up so we use the plus sign fr v ur v 1 34034134o 400 Hz 440 Hz More neat stuff that s not on your exam l How can we measure the speed of objects in distant space The light waves are doppler shifted they appear to be different colors depending if they are moving towards us or away from us You have to use relativity to calculate the shift in wavelength of light What is a shock wave This is when the speed of the object is faster than the speed of the wave in the medium breaking the sound barrier The waves pile up behind the source to form a shock wave or sonic boom Source moving faster than wave speed in water End of Chapter Questions for review 25 41 43 45 59 61 63 75 77 79 95 101 105 Chapter 16 Superposition and Standing Waves 523 H7 1569 H7 2532 i 39 2819 H7 3104 Hz 7 H 5323 Hz 5435 H7 3866 H7 J z 4709 H7 1137 i Z PrOf Simon CapstiCk I I I I I I 7263 117 gt571 I 7 7892 H7 72 i I 8002 i l7 873 liz Standing wave patterns inside musical instruments Superposition of waves The superposition WF39L principle when 2 or b more waves overlap the IJL resultant wave is the b algebraic sum of the individual waves Wave interference When two harmonic waves overlap of the same Wave 2 wavelength they add together Constructive interference Vv ave 1 when the two waves are In phase same phase Resultant wave constant they create a Constructive interference larger wave Wave 2 Destructive Interference Resultant wave when the two waves are 180 degrees or1T radians out of xquot quotN x s xquot l 4 phase then they Interfere z x A I s destructiver a x x nquot Wave 1 Destructive interference B eat frequencies b What if the frequencies are different The resultant wave has a beat frequency the modulated amplitude volume for sound waves of the new wave has a different frequency that is equal to the difference in frequencies fbeat Af f2f1 This is how musical instruments can be tuned Beat frequency demo n I l I 39 I l III Iulhlh39 I I y u 39 391quot II t Adding together 2 frequencies produces a beat frequency determined by the envelope of the new wavefunction AAA 1mm lll flVUVtVV The amplitude changes as a f 3 function of time llll UVV
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