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Circuitous definition of charge ?

  1. Aug 31, 2014 #1
    Hello, I've been trying to pin-point the precise definition of charge, but I'm having difficulty. I asked my Professor at college what 'charge' is exactly, and he thought carefully for about a minute, and replied that he really has no idea.

    The best I can come up with is the following serious of arguments :

    1) q= it

    Charge is current and the time it takes that current to move, which begs the question:what is current?

    2) i = V/R

    Current is the potential drop V across a resistor R. So what is a potential drop ?

    3) V= kq/r

    Potential drop is the the movement of charge q across free space k in a distance r.

    I think you can begin to see the circuitous reasoning here. This eventually leads to :


    ....... just by algebraic reasoning.

    Help ! What did I do wrong, and can someone seriously answer the question on what a 'charge' really is -- I mean I know a charge has positive and negative, and field lines flow into negative etc, but what is a charge ?
  2. jcsd
  3. Aug 31, 2014 #2

    Simon Bridge

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    Charge is the measure of the amount that a substance behaves electrostatically.
    i.e. it is a phenomenon, not a thing as such.

    However - charge does not have a definition in the sense that force has. It is a material property that we describe in terms of interactions. It's like asking for a definition of space or matter.

    Your three equations are for different situations, so they should not be used together.
    To find physical relations, first start with the physics, not the maths.
  4. Sep 1, 2014 #3


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    Staff: Mentor

    Charge is a property of particles. By definition, an electron has a negative charge (with some arbitrary fraction of a Coulomb assigned to it), the other particle charges then follow from observation.
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