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Can there be a charge configuration in space such that at any instant of time I can change the electric field at one and only one point?

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  • $\begingroup$ Electric fields propagate at the speed of light--so if you can stop time you can change the electric field at only one point. $\endgroup$ – Dale Aug 17 '11 at 8:41
  • $\begingroup$ How would you be changing the electric field? $\endgroup$ – David Z Aug 17 '11 at 9:01
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The electric field obeys Maxwell's equations and in particula the Gauss's law. This means that $\rm div E \sim \rho$. If you change the field at only one point, this will introduce an infinite divergence and consequently infinite density. In other words, you'd have to introduce a point charge. But then the field $E$ itself will diverge at that point. So the answer is no, you can't do this.

In general, the allowed configurations are continuous except at boundaries of objects (where $E$ has to jump to account for charges in the material) and at point charges (where the field diverges).

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