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Homework Help: Dirac Delta function question

  1. Feb 2, 2009 #1
    I cannot get the answer as from the solution manuel.

    2vl5jd0.jpg

    Please tell me what am I assuming wrong.
    Thanks
     
  2. jcsd
  3. Feb 2, 2009 #2

    Dick

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    Just showing that the value of a function is '-infinity' at a point and zero otherwise doesn't tell you it's a delta function. Apply the divergence theorem to grad(1/r) on a sphere around the origin to figure out how much 'charge' is there.
     
  4. Feb 2, 2009 #3
    I understand that and I showed in my own answer. What I don't get is where the 4[tex]\pi[/tex] come from!!
    Thanks
     
  5. Feb 2, 2009 #4

    Dick

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    No, all your answer said was the value at zero is '-infinity' (I'm putting that in quotes because I'm not even sure it makes sense). I said that DOESN'T mean it's a delta function. The 4*pi comes from checking the flux through a sphere around the origin. It comes from the 4*pi in the formula for the area of a sphere.
     
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