# A barking dog delivers about 1.0 mW of power, which is assumed to be

1. Jun 21, 2014

### chemistrymole

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

A barking dog delivers about 1.0 mW of power, which is assumed to be uniformly distributed in all directions. What is the intensity level in decibels at a distance 5.00 m from the dog? The threshold of human hearing is 1.0 × 10-12 W/m2.

2. Relevant equations

I=P/A A is 4pi(r^2)

3. The attempt at a solution

The only part I am missing is converting the 1 mW to something else so I can plug in the equation above. I tried the 10*log(xxxxxxxx) formula no luck.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 21, 2014

### Staff: Mentor

The power all goes through each spherical surface surrounding the dog. If the sphere has a surface area of 1m^2, then the power flux density is 1.0mW/m^2. If the sphere is a little bigger, and has a surface area of 2m^2, then the power flux density 1.0mW/2m^2 = 0.5mW/m^2.

Does that help?

3. Jun 21, 2014

### chemistrymole

No still lost and confused.

Can someone please explain equations further I am not seeing how it connects to the variables given in the question.

4. Jun 21, 2014

### haruspex

As the sound waves of the bark radiate out from the dog, the 1mW of power (P) gets spread over a progressively larger area (A). At a distance of 5m, what area is it spread over?

5. Jun 21, 2014

### chemistrymole

Do I have to convert 1 mW to W?

So would my setup be I = 1/pir^2?

I think my main formula template is I=P/A

6. Jun 21, 2014

### chemistrymole

Thanks everyone I found a solution that shows me how to do it. Now I actually understand it and know how the units work.