# Using Beer-Lambert law to calculate light intensities

Chemistry Asked by lblindner on December 23, 2020

Supposing the mean absorption coefficient of seawater in the visible region is $$pu{0.8 m-1}$$, calculate the depth at which a diver will experience half the surface light intensity.

I know that you have to use $$A = -log left(dfrac{I}{I_o}right) = epsilon cl$$ but I’m not sure how to proceed

In my opinion, Beer–Lambert law is no use. I would rather write

$$frac{mathrm dI}{I,mathrm dl} = pu{0.8 m^-1},tag{1}$$

which leads to the integrated formula

$$lnleft(frac{I_0}{I}right) = 0.8 l.tag{2}$$

And, if $$displaystylefrac{I}{I_0} = 0.5,$$ the corresponding depth is

$$l = frac{ln 2}{0.8} = pu{0.846 m}.tag{3}$$

Answered by Maurice on December 23, 2020

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