1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Deriving electromagnetic fieldfor point charge

  1. Feb 21, 2013 #1


    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.

  2. jcsd
  3. Feb 21, 2013 #2


    User Avatar

    oh I've got it. Forgot the minus sign in the triple cross product rule :$
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook