# Math Help - Sound Intensity Problem

1. ## Sound Intensity Problem

At a concert, the loudness of sound, L, in decibels, is given by the equation L=10log(I/I_o), where I is the intensity, in watts per square metre, and I_o, is the minimum intensity of sound audible to the average person, or 1.0 x 10^-12 W/m^2.

a) The sound intensity at a concert is measured to be 0.9 W/m^2. How loud is the concert?

My answer (that is correct); 119.54 dB

b) At the concert, the person beside you whispers with a loudness of 20 dB. What is the whisper's intensity?

My attempt: (but it is wrong)
20+119.54=10log(I/10^-12)
Then I solved for I, to get T=89

c) On the way home from the concert, your car stereo produces 120 dB of sound. What is its intensity?

I did not get this answer either, but tried to do it like b...

Help on parts b and c please

2. Originally Posted by skeske1234
b) At the concert, the person beside you whispers with a loudness of 20 dB. What is the whisper's intensity?

My attempt: (but it is wrong)
20+119.54=10log(I/10^-12)
Then I solved for I, to get T=89
I don't think you're supposed to add the two decibel levels 20 and 119.54. Just put 20 on the left side:
20=10log(I/10^-12)

Now solve for I.

$2=log(I/10^{-12})$
$10^2 = 10^{log(I/10^{-12})}$
$100 = \frac{I}{10^{-12}}$
$I = 10^{-10}$

For part c, the equation would be
120=10log(I/10^-12). Solve for I.

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