Calculating Energy Received by a Human Eardrum at Threshold of Hearing

[Cheezay]

Homework Statement

The radius of a typical human eardrum is about 4.10 mm. Calculate the energy per second received by an eardrum when it listens to sound that is at the threshold of hearing, assumed to be 1.04E-12 W/m^2.

Homework Equations

I=P/A

The Attempt at a Solution

First i start by converting 4.10mm to m, for which i get .0041m.

The rest seems simple:
Intensity= 1.04E-12 W/m^2
Area= 4(pi)(r^2)

plugging in my numbers i get 1.04E-12 W/m^2= P/.000211

Then I solve for P, because power=Energy per time and is expressed in W.
This problem seems like it should be simple. I really have no idea where i am making the mistake, any help would be greatly appreciated.

 

[cepheid]

I'm assuming the eardrum is roughly circular. Hence:

$$A = \pi r^2$$

 

[Cheezay]

Thanks for the help, that's what i was doing wrong :)