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Inverse-square law

  1. Oct 29, 2008 #1
    If the intensity of electromagnetic radiation (I) is equal to the power emitted (P) divided by the area of the sphere (4pi(r^2)) that it radiates, why is the inverse-square law 1/(r^2) instead of P/(4pi(r^2))? Shouldn't the radiation emitted propagate isotropically in all directions (sphere) instead of anisotropically (cube)? I apologize for the notation; I don't know how to write in latex. Thank you.
  2. jcsd
  3. Oct 29, 2008 #2


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    the [itex]4 \pi[/itex] factor can just be folded into the "k" or "G" factor we see in inverse-square laws. either way, they're inverse-square.

    but, i agree with your sentiments, which is why i think that more natural Planck Units would be those that normalize [itex]4 \pi G[/itex] instead of just [itex]G[/itex] and it would be better to choose a natural unit of charge that would normalize [itex]\epsilon_0[/itex] instead of normalizing [itex]4 \pi \epsilon_0[/itex].
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