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Homework Help: EM waves; max value of electric field

  1. May 30, 2003 #1


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    What is the max value of the eletric field at a distance 2.5m from 100W light bulb?

    I have the formula E_o = [squ]2S/e_oc. This is what i have so far...
    E_o = [squ]2(100W)/(8.85x10^-12C^2/Nm^2)(3x10^8m/s) = 274V/m.

    My calculations are not right can someone help me with solving for this, plz?

    Dx :wink:
    Last edited by a moderator: May 30, 2003
  2. jcsd
  3. May 30, 2003 #2
    Wrong equation Dx.
    S, the poynting vector, is not the power of the bulb. Rather, Power, P = S(4[pi]r^2). From this you can derive an eqn. which includes r.

    Last edited: May 30, 2003
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