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Electromagnetic waves

  1. Dec 21, 2015 #1
    1. The problem statement, all variables and given/known data
    Calculate electric field and magnetic field produced by radiation emitted by a 100 W bulb at a distance of 1 m if radiation efficiency is only 5%.

    2. Relevant equations

    3. The attempt at a solution
    I only know how to find intensity due to the bulb:
    I = P/4πr2 = 5/4π W/m2
    I have absolutely no idea how to find the electric and magnetic field from that information.
    I do know that B = E/c, so I just need to find one of those.
  2. jcsd
  3. Dec 21, 2015 #2


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    Staff: Mentor

    Look in your textbook (or Google) for an equation for the power (density) carried by an electromagnetic wave. It can be expressed in terms of either the electric or magnetic field. It's a standard equation so it should be in your book if it has that exercise.
  4. Dec 21, 2015 #3
    Got it, I = (εE^2)(c).
    No, it's not a textbook problem. And my book doesn't have much on this.
  5. Dec 21, 2015 #4


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    Staff: Mentor

    Well, it sure looks like a textbook or exam problem. I've given similar problems to students many times. :oldwink:
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