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Power and EM waves

  1. Jun 23, 2013 #1
    1. The problem statement, all variables and given/known data
    A plane polarized electromagnetic wave propagates
    with Erms = 30 V/m. What is the power transmitted to
    a circular disk of radius r = 2m, if all of the light is
    absorbed by the disk and S is perpendicular to the
    disk?


    2. Relevant equations
    There is a passage that goes along with this that states that I =Erms^2/(cμ0), and that I = P/A. u0 = 4 × 10–7 N•s^2/C^2.



    3. The attempt at a solution
    Basically, I plugged in the values of Erms and μ0 into the Intensity equation and then multiplied by A (pi*4) to get 94.2.

    But the answer key says the answer is 30 and that instead of multiplying by pi*r^2, you multiply by r^2. Please help!
     
  2. jcsd
  3. Jun 23, 2013 #2

    Simon Bridge

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  4. Jun 23, 2013 #3
    Where is the other pi?
     
  5. Jun 24, 2013 #4

    Simon Bridge

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    You'll just have to try to understand the problem to see.
     
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