# Homework Help: Calculating intensity

1. Aug 5, 2010

### dobbinatrix

I need to calculate the intensity of a 10000 lux light source travelling through 3.3 cm of water.

I have attempted to solve this using the equation I=Ioe-A where i is the intensity, Io is the initial intensity, A is the absorbance calculated as the water attenuation coefficient times the depth, using the water attenuation coefficient of 0.23222 (this could be wrong?)

This equation can be simplified into I=Io*10^-A
however when i plug my numbers into this i seem to get I=10000*9.9 which means that the intensity has increased tenfold in 3cm of water.
Somthing tells me im wrong...

Any help would be greatly appreciated

P.S. thanks to ehild for last response

2. Aug 5, 2010

### ehild

How could you get a number greater than 1 as the result for 10^(-A) (A>0)?

ehild