I am a beginner in electrostatics.

I don't understand the below:

When we have a set of charges, those charges exert a force on the test charge but what I don't understand is how are these set of charges at rest? Isn't this against the Coulomb's law?

Won't each charge affect each other causing them to move and not letting them to be in rest?


1 Answer 1


Remember that for charges to flow, we require a potential difference, and a low resistance path(not an insulator). So, charges can't flow in case of insulators, when no free charges are available, even if there is a difference of potential.

  • $\begingroup$ Thank you! But in the superposition principle the set of charges exist in free space, how do we understand that phenomenon? $\endgroup$ Commented May 31, 2019 at 7:32
  • $\begingroup$ It is just to simplify things! The focus is to demonstrate the theorem and not to consider the movement of charges. $\endgroup$
    – Tojra
    Commented May 31, 2019 at 8:11
  • $\begingroup$ The superposition principle and the electrostatic forces will always be present. It depends whether you want to consider the motion or not. But practically the case is as I have explained in the answer. $\endgroup$
    – Tojra
    Commented May 31, 2019 at 8:13
  • $\begingroup$ Thank you so much for explanation. It helped me get a clear idea. $\endgroup$ Commented May 31, 2019 at 8:30

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