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Homework Help: Energy in a wave

  1. Mar 30, 2009 #1
    1. The problem statement, all variables and given/known data
    How much energy is transported across a 1.15 cm2 area per hour by an EM wave whose E field has an rms strength of 36.5 mV/m?

    2. Relevant equations
    u (energy per unit volume) = [tex]\epsilon_0 E^2 \frac{J}{m^3}[/tex]

    3. The attempt at a solution
    Since I have u = 8.85*10-12*(36.5*10-3)2 J/(m^3). I multiply this by the given area (1.15 cm2) which gave me units of J/m. The only other thing that seems to make any sense that would get me to J/h would be to multiply by the speed of light in meters per hour.
  2. jcsd
  3. Mar 31, 2009 #2


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    Homework Helper

    Hi Queue, that sounds reasonable to me - multiplying by the speed of light gives the power crossing the surface area. Transferring the speed to m/hr is equivalent to finding the power transfer in J/s, using m/s, then multiplying by 3600s to find the total energy trasnferred in an hour
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