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I Coulomb's law

  1. Sep 23, 2016 #1
    According to Coulomb's law, the electric force between two, equal in magnitude and opposite in direction, charges depends on the distance between them, and as they get close to each other, the force increases and the distance decreases. At the position when they get stuck with each other, the force will be maximum, but what would the distance be?
    My approach is that it will be the distance between the two centers of the two charges, is that correct?
  2. jcsd
  3. Sep 23, 2016 #2


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    Homework Helper

    Charge is property of bodies and particles, it does not exist by itself. You can not speak about the distance between charges.
    If you have two charged spheres,and they get stuck, the distance between the centers is equal to the sum of the radii of the spheres.
  4. Sep 23, 2016 #3


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    Staff: Mentor

    Coulomb's law in the common form that you're using is for point charges, idealized objects with no size at all. Thus, no matter how close they are to one another, your charges won't touch and stick together.

    Of course no real charged object is an ideal point particle; it has to have a surface and some size and shape. If you bring two of these close enough to touch, you'll have to use the more complicated integral form of Coulomb's law (google for "Coulomb's law integral") to calculate the force between them, and to do that you need to know the shape of both objects and how the charge is distributed within them.
  5. Sep 24, 2016 #4
    Actually, the experiment was two charged balloons brought to stick on each other after hanging them over a rod using two strings with the same length, and they also brought to be in an equilibrium condition, in which we found the electric forces using newton laws. But, when I wanted to measure the charges on the balloons
    (assuming they have equal charges) I got confused about the distance between them as they are stuck?
    So, I assumed it will the distance between their centers.
  6. Sep 24, 2016 #5


    Staff: Mentor

    Yes, that is correct for spherically shaped charges (which from context is what I believe that you are considering)
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