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Centre of Charge analogous to Centre of Mass, Valid Concept ?

  1. Jul 7, 2013 #1
    I want to know whether I can use a point where all charge of a body can be assumed to be concentrated. Obviously such a point exists. I want to know whether it'll be the same point as centre of mass [as both are scalars and their integration SHOULD yield the same result]

    For example, if a half ring [semicircle] has a charge 'Q' uniformly distributed over it and a radius 'R', can I assume all of this Q to be effectively centred at '2R/∏' [location of centre of mass] from its centre? :bugeye:
  2. jcsd
  3. Jul 7, 2013 #2
    First, the center of mass is not a scalar - it is not a mass, it is a position. Furthermore, the charge and mass might not have the same density everywhere, so the two might be centered around different positions. Say you have two spheres, one i charged, one is not. Then the CoM would be between the spheres (for some appropriate density of the spheres) but the 'charge center' would be in the middle of the charged sphere.

    For your second question, the answer, I believe, is "no, not in general". If you're talking about spherically symmetric things then yes (look up Gauss law of "something to do with this"), but anything else is more tricky than that.
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