# Help with a Wave Intensity Problem

1. Nov 29, 2007

### Smx_Drummerboy

[SOLVED] Help with a Wave Intensity Problem

Hello all, here is a problem that relates to Wave Motion, more specifically Wave Intensity I believe:

The figure shows two observers 20m apart on a line that connects them and a spherical light source.
Figure: (The best I know to do)

(Person A)<----------20m----------->(Person B)<----------?m---------->(Light Source)

If the observer nearer the source measures a light intensity 45 % greater than the other observer, how far is the nearer observer from the source?

Relevant Equations:
I = [ latex ] \frac{P}{(4pi(r^2))} [ /latex ]

My initial thought was to state the following:
Ia = .45Ib and da = x +20 and db = x

Then plug in all the values given, the P's cancel, and I thought I'd be left with an answer. I got 41m, apparently that isn't right. I've been working on this problem for nearly an hour and a half.

Any suggestions?

Last edited: Nov 29, 2007