# Homework Help: Pressure Amplitude

1. Dec 11, 2007

### Jtappan

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

(a) What is the pressure amplitude of a sound wave with an intensity level of 124.5 dB in air?

_____ N/m2
(b) What force does this exert on an eardrum of area 0.520 10-4 m2?

_____ mN

3. The attempt at a solution

if P is amplitude of pressure, then sound intensity (I) is proportional to P^2
I/Io = (P/Po)^2
dB = sound intensity level = 10 log[I/Io]
124.5 = 10 log[I/Io] = 10 log[P/Po]^2 = 20 log(P/Po)
log(P/Po) = 124.5/20 = 6.225
P = Po [10]^6.225
Po = reference pressure amplitude for human ear = 2*10^-5 N/m^2
P = 2*10^-5*[10]^6.225
P = 33.576 N/m^2
----------------
Force on eardrum = P * area = 33.576*0.52*10^4 N
F = 1.746 milli N

This is what I did. But it is not giving me the correct answer...can anyone help me?

2. Dec 11, 2007

### dlgoff

The given eardrum area is 0.520*10^-4? But in your force equation (Force on eardrum = P * area = 33.576*0.52*10^4 N) you have it as 0.52*10^4.