# Soundwave Intensities and power

1. Jan 29, 2012

### chelsea123

1. The problem statement, all variables and given/known data

1. Question : A point source emits 34.0 W of sound isotropically. A small microphone intercepts the sound in an area of 0.510 cm2, 185 m from the source. What is the sound intensity at that distance?
What is the power intercepted by the distance?

2. Relevant equations

I=P/a,P=IA

3. The attempt at a solution

so far i have gotten the intensity as I=P/A,
I=340W/(5.10*10^-3)+4pi(185)^2
I=7.91*10^-5 W/m^2

However for the second part of the question to calculate power, it is not correct. I use P=IA
with the same area but it will not work properly:
P=(7.91*10^-5W/m^2)(5.10*10^-3m2 + 4pi(185m)^2
P=34.0 W (which is incorrect)

Where is the flaw in this equation?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 30, 2012

### Spinnor

For the first part,

I_atmic = P/A where P and R are given in the problem, and A = 4∏R^2

For the second part P_atmic = [I_atmic]a = Pa/A where a is the area of the mic.