# Light intensity in matter

1. Apr 22, 2015

### sunmaggot

1. The problem statement, all variables and given/known data
An electromagnetic wave with frequency 65.0Hz travels in an insulating magnetic material that has dielectric constant 3.64 and relative permeability 5.18 at this frequency. The electric field has amplitude 7.20×10−3V/m.

What is the intensity of the wave?

2. Relevant equations
I = S average = 1/2 ε0 c Emax2

3. The attempt at a solution
the above equation is what I only have from my textbook, and it is for vacuum case. However, in the question, it has dielectric constant and relative permeability. I tried changing c into the light speed in the medium, not correct. I tried using equation from wiki, that is, times refractive index in the above equation, doesn't work. I tried simply ignore the refractive index problem, and doesn't work.

2. Apr 23, 2015