reed2100
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Homework Statement
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. Homework Equations
Intensity = Power/area -> I=P/A
I = E^2 / (2 * μ-naught * speed of light)
Energy = power * time
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.