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Old Nov 22nd 2009, 01:02 AM   #1
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intensity

A sound source emits energy uniformly to all directions . At certain frequency , its intensity at a distance of 1.0m from the source which is equivalent to the amplitude of molecular oscillation of 70/mu m is 1.0\times 10^{-5} Wm^{-2} . Assuing there is no enerygy loss , determine the intensity of sound .

Isnt that the intensity 1.0\times 10^{-5} Wm^{-2} ? Is this the intensity of sound or energy ? i am a little confused here .

Btw , am i the only one having problems with the latex here .
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Old Nov 22nd 2009, 01:06 AM   #2
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Hi,

I'll answer you later today, my son is moaning he wants this laptop.
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Old Nov 22nd 2009, 02:49 AM   #3
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At 1m the intensity and sound pressure will be 11 dB lower than the sound source (SWL) . The ref level you are thinking of is (2*10^-5) for sound pressure.

Example sound pressure:

80 dB = 0.2 Pa

20 log.(0.2/0.00002)= 80

Example intensity:

0.0001 W/m^2 =80 dB

10 log.(0.0001/(10^-12))=80

Sound source = 91 dB SWL

sound pressure = 91-((20log distance)+11) = 80
91-((20log 1)+11)=80

Intensity =

Sound source Watts/(4*pi*r^2) = W/m^2 at distance.
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Old Nov 22nd 2009, 04:21 AM   #4
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Originally Posted by Paul46 View Post
Hi,

I'll answer you later today, my son is moaning he wants this laptop.
No worries .
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