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November 01, 2025, 09:38:23 am
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Author Topic: working out the Intensity at a distance  (Read 643 times)  Share 

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Gordo

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working out the Intensity at a distance
« on: November 09, 2010, 01:05:00 pm »
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An isolated siren emits sound of 3000Hz uniformly in all directions. At a point 20m from the siren, the sound intenisty is measured to be 1.0 x 10^-3

The sound intensity is measured at a distance of 60m what is the sound intenisty?

I have totally forgot how to do this question help?
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coletrain

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Re: working out the Intensity at a distance
« Reply #1 on: November 09, 2010, 01:14:02 pm »
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inverse square law
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Chavi

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Re: working out the Intensity at a distance
« Reply #2 on: November 09, 2010, 01:15:03 pm »
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Remember that Intensity = Power/Area

Mathematically, Area in this case is the surface area of a sphere, so just find the derivative of (4/3pir^3) and you get A=4pir^2
 
Alternatively, for this question, just use I1/I2 = (r2/r1)^2 to find I2 (i.e. the 2nd Intensity)
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qshyrn

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Re: working out the Intensity at a distance
« Reply #3 on: November 09, 2010, 01:18:16 pm »
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Quote from: Gordo on November 09, 2010, 01:05:00 pm
An isolated siren emits sound of 3000Hz uniformly in all directions. At a point 20m from the siren, the sound intenisty is measured to be 1.0 x 10^-3

The sound intensity is measured at a distance of 60m what is the sound intenisty?

I have totally forgot how to do this question help?
so distance is 3x.... intensity = divide by 9
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