1. The problem statement, all variables and given/known data A sinusoidal electromagnetic wave from a radio station passes perpendicularly through an open window that has area of 0.700m2 . At the window, the electric field of the wave has an rms value 2.30×10−2V/m . How much energy does this wave carry through the window during a 30.0s commercial? 2. Relevant equations Intensity = Power/area -> I=P/A I = E^2 / (2 * μ-naught * speed of light) Energy = power * time 3. The attempt at a solution First find I since I am given all values needed ? I = [ (2.3 * 10^-2 )^2 ] / [ 2 *4π * 10^-7 * 3 * 10^8 ] I = 7.01 * 10^-7 Power = Intensity * area Power = 7.01 * 10^-7 * (.7) Power = 4.91 * 10^-7 Energy = power * time Energy = 4.91*10^-7 * (30) Energy = 1.47 * 10^ -5 Joules That's incorrect and I'm having trouble figuring out where I went wrong, as I used the same approach for a similar problem and it worked. The difference between problems was that I wasn't given an rms value, instead I was just told the magnitude of the field if I remember correctly. I thought the rms was just root mean square and was just another way of expressing an "average" -ish value. Do I need to use μ instead of μ naught because it's in air and technically not vacuum? That would confuse me as well because I did a problem in this vein that involved high energy waves through flesh to eliminate cancer cells, and μ naught worked fine. I wouldn't think the program would suddenly switch it's expectations of what simplifications to use for the sake of the course level. Any and all help is greatly appreciated.