# Find Pressure amplitude from given decibels

1. Nov 18, 2011

### Angie_Agnes

1. The problem statement, all variables and given/known data
A sound wave has an intensity level of 49 dB. What is the pressure amplitude of this wave?

Po= 2x10^-5
2. Relevant equations

β=10log(I/I0)
I≈P^2

3. The attempt at a solution
I can't figure out why I'm getting this problem wrong. So I set it up, 49=10log(I/I0)
-> 4.9=log(I/I0) -> 10^4.9=(I/I0) From there, I replaced the intensity for pressure amp (equation 2) -> p=(2*10^-5)√(10^4.9)
Pamp=.0056Pa

??

2. Nov 18, 2011

### I like Serena

Hi Angie_Agnes!

You calculation looks good.
Any reason to doubt your result?

3. Nov 19, 2011

### Angie_Agnes

yes, it's online homework and says it's wrong :(

4. Nov 19, 2011

### I like Serena

Well, I think you have to tweak your result a bit then.
I believe it is numerically correct, but these online homework sites can be a bit difficult with the exact phrasing.
Btw, I'm assuming you did not make a typo in the problem statement...

5. Nov 19, 2011

### Angie_Agnes

I copied and pasted the question, so no typo.... I typed it in as .005 Pa and .006Pa and both came up wrong. Frustrating!

6. Nov 19, 2011

### I like Serena

With 2 significant digits in 49 dB, it should be 0.0056 Pa or 5.6 mPa.
I can't make anything else from it.

7. Nov 19, 2011

### Angie_Agnes

THANK YOU! got it right as .0056Pa. Awesome!

8. Nov 19, 2011

### I like Serena

9. Nov 19, 2011

### Angie_Agnes

I looked back at my past answers, I had entered it .005 and .006 at first, before entering it finally as .0056.

10. Nov 19, 2011

### I like Serena

All is well that ends well!