1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Intensity of Electromagnetic Waves

  1. Mar 25, 2012 #1
    1. The problem statement, all variables and given/known data
    A plane monochromatic electromagnetic wave with wavelength λ = 2.2 cm, propagates through a vacuum. Its magnetic field is described by
    [itex]\vec{B}[/itex] = (Bx[itex]\vec{i}[/itex] + By[itex]\vec{j}[/itex])cos(kz+ωt)
    where Bx = 1.8E-6 T and By = 3.8E-6 T, and i-hat and j-hat are the unit vectors in the +x and +y directions, respectively.

    What is I, the intensity of this wave?

    2. Relevant equations
    I = P/A = (1/2)cεoE^2
    k = (2π)/λ
    ω = ck
    Bo*c = Eo

    3. The attempt at a solution
    I found frequency to be c/λ = 13.63GHz.

    I have tried setting t to zero in the given equation and plugging in k and ω to find B, then multiplying that by the speed of light to find E.
    I then plugged that into I = (1/2)cεoE^2, but that gave me the wrong answer.

    I've also tried adding to the two vectors and assumed that equaled Bo (which I don't think it does), and used Bo = (√2ZoI)/c where Zo = 377 ohms.
    I've tried <B^2> = (Bo^2)/2 as well.

    Is there an important equation I'm missing?
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted