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Deriving electromagnetic fieldfor point charge

  1. Feb 21, 2013 #1

    nos

    User Avatar

    Hi all,

    I was going through the derivation for the electromagnetic field of point charges by Griffith(Introduction to electrodynamics page 437).

    I'm missing minus sign somewhere:

    The book says that:[itex]\nabla(\vec{n}\cdot\vec{v})=\vec{a}(\vec{n}\cdot \nabla tr)+\vec{v}-\vec{v}(\vec{v}\cdot\nabla tr)-\vec{n}\times(\vec{a}\times \nabla tr)+\vec{v}\times (\vec{v}\times \nabla tr)[/itex]

    Using the rule for triple cross products gives:

    [itex]\vec{v}+(v^{2}-\vec{n}\cdot\vec{a})\nabla tr[/itex]

    However is should be:

    [itex]\vec{v}+(-v^{2}+\vec{n}\cdot\vec{a})\nabla tr[/itex]


    I'm sure Im missing something.

    Thanks
     
  2. jcsd
  3. Feb 21, 2013 #2

    nos

    User Avatar

    oh I've got it. Forgot the minus sign in the triple cross product rule :$
     
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