PHY 231 1 PHYSICS 231 Lecture 35: Sound Remco Zegers Question hours: Thursday 12:00-13:00 & 17:15-18:15 Helproom Hello Darkness, my old friend I’ve have come to talk to you again, Because a vision softly creeping, Left its seed while I was sleeping, And the vision that was planted in my brain Still remains, Within the sound of silence. Paul Simon-1964
PHYSICS 231 Lecture 35: Sound . Hello Darkness, my old friend I’ve have come to talk to you again, Because a vision softly creeping, Left its seed while I was sleeping, And the vision that was planted in my brain Still remains, Within the sound of silence. Paul Simon-1964. Remco Zegers - PowerPoint PPT Presentation
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Hello Darkness, my old friendI’ve have come to talk to you again,Because a vision softly creeping,Left its seed while I was sleeping,And the vision that was planted in my brainStill remains,Within the sound of silence.
The speed of soundDepends on the how easy the material is compressed (elastic property) and how much the material resistsacceleration (inertial property)
v=(elastic property/inertial property)
v=(B/) B: bulk modulus : density
The velocity also depends ontemperature. In air:
v=331(T/273 K)
so v=343 m/s at room temperature
PHY 2314
Quick quizThe speed of sound in air is affected in changes in:(more than one possible)a) wavelengthb) frequencyc) temperatured) amplitudee) none of the above
answer c)
PHY 2315
Intensity
Intensity: rate of energy flow through an area
Power (P) J/s A (m2)
I=P/A (J/m2s=W/m2)example: If you buy a speaker, it gives power output
in Watts. However, even if you put a powerful speaker in a large room, the intensity of the
exampleA machine produces sound with a level of 80dB. Howmany machines can you add before exceeding 100dB?1 machine80 dB=10log(I/I0)8=log(I/I0)=log(I/1E-12)108=I/1E-12I1=10-4 W/m2
ExampleA person living at Cherry Lane (300 m from the rail track)is tired of the noise of the passing trains and decides tomove to Abbott (3.5 km from the rail track). If the soundlevel of the trains was originally 70dB (vacuum cleaner), what is the sound level at Abbott?
vobserver: positive if moving towards to sourcevsource: positive if moving towards the observer
PHY 23122
exampleA police car using its siren (frequency 1200Hz) is drivingwest over Grand River with a velocity of 25m/s. Youare driving east over grand river, also with 25m/s.a)What is the frequency of the sound from the siren thatyou hear? b) What would happen if you were also driving west?vsound=343 m/s