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Just like while calculating gravitational potential energy, we take earth's potential as zero and with respect to that we calculate potential at a point. Similarily in electrostatics why can't we take source charge's potential as zero and not infinity.

Also will the potential at a point a point $R$ near charge be different if we take zero Potential at source charge or at infinity?

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  • $\begingroup$ The potential is indeed taken to be zero when calculating the gravitational potential energy $-GMm/r$. $\endgroup$ May 8 '20 at 14:52
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You can place the zero of electrostatic potential almost anywhere you want. You can't place the zero at the location of a point charge because the potential is not defined there. But a point charge is an idealization. For all practical situations you can place the zero anywhere. But it's much more convenient to place it at infinity. That way the zero is the the same "place" (if infinity is a place) for all objects in question.

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  • $\begingroup$ why dont we take zero at infinity while deriving gravitational potential ? $\endgroup$ May 8 '20 at 13:20
  • $\begingroup$ i also dont understand how can we bring a charge from infinity PRACTICALLY $\endgroup$ May 8 '20 at 14:24
  • $\begingroup$ @JoelRodriguez We often do take the zero at infinity for the gravitational potential, for example in the derivation of escape velocity. The only reason we take the zero to be on the floor or on the ground or on the table is for convenience. Anywhere you use $mgh$ you can also use Newton's Law of gravity with the zero of potential at infinity, You'll get the same answer (actually an imperceptibly better answer) at the expense of unnecessary math. It's definitely worth it to do the analysis both ways ($mgh$ and Newton) to see how $mgh$ is accurate near the Earth. Very educational. $\endgroup$
    – garyp
    May 8 '20 at 16:24
  • $\begingroup$ @JoelRodriguez Here's what I meant by practical. Suppose I have two spherical charged objects. If I take the zero of potential at the surface of one of them, it's impractically and unnecessarily difficult to calculate the potential at the surface of the other by calculating the force on a test charge between them. I think you'd end up implicitly setting zero at infinity without realizing it. In electrical circuits the only way to make progress is to set zero somewhere in the circuit. Setting zero at infinity is impractical in that case. $\endgroup$
    – garyp
    May 8 '20 at 16:28

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