How Does Electromagnetic Wave Intensity Decrease with Depth?

[iontail]

Homework Statement

Show that intensity of radiation(EM wave) falls off with depth z
as
I(z)= Ie^(-2niwz/c)

where I = initial intensity
and ni=complex paert of refractive index

Homework Equations

I have tried the solving the solution using poynting vector.


I have been pondering over the question over the last two days without any success. I think i am making it more complicated than it needs. to be. I would appreciate it if you point me in the right direction .

 

[turin]

Determine the electric field. You are probably supposed to assume that an EM wave is normally incident on the surface.