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I Power delivered to a charge

  1. May 23, 2016 #1
    Suppose some charge and current config is present which at time t produces fields
    E and B. In the next instant dt the charges
    move around a bit.
    Work done on the charge q
    dW/dt= qE.v

    Now the question is q has also contribution in the field E. How the charge is exerting force on itself?
  2. jcsd
  3. May 23, 2016 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Unless your charge has some actual and variable distribution in space (then you probably need integration), ignore the field of a given charge to calculate how that charge moves.
  4. May 23, 2016 #3
    The problem: there is a charge and current configuration. Electric field and magnetic field originates from this configuration. The charges now move under the influence of the field in time dt. What is the work done by the field?
    While calculating the work done we take force as ∫ρ(E+v×B).vdt dV. Why the same field originating from ρ exerting force on it?

    We are not ignoring the field of the charge on which we are calculating force, the problem is the whole field is taken during calculation.
    I am following the book written by Griffiths.
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