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if i charge small object by removing electrons and put that object in the middle of huge vacuum chamber (million of light years in size) does the electric field lines of that charged object still be able to reach the walls of vacuum chamber? and the electrons in walls (or air outside) will experience force? and if so than at what speed? faster than light?

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3 Answers 3

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The range of the Coulomb force is infinite (the force between two charges $Q_1, Q_2$ separated by a distance $r$ is given as $F = \frac{Q_1 \, Q_2}{4 \pi \epsilon_0 r^2}$), with the implication that the photon has zero (rest) mass. However if you were to suddenly create (say) a positive then the "news" about this would travel at the speed of light, so that any other charges wouldn't know about this at the instant you created the charge, but rather would have to wait some time for the "news to filter" through. Of course, the size of field get's smaller as you get further away and it will become more difficult to detect.

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  • $\begingroup$ but what about Inverse Square Law ? the field will multiply itself with distance from a sphere to be infinite (this lead to free energy?) or cease to exist or what? $\endgroup$
    – szufla
    Commented Apr 15, 2016 at 12:00
  • $\begingroup$ have updated answer, the size of the field get smaller at larger distances, and so its influence on other charges will be less. $\endgroup$
    – jim
    Commented Apr 15, 2016 at 13:31
  • $\begingroup$ So we can assume that electric field has its limits and at long distances will vanish. thanks for answer. $\endgroup$
    – szufla
    Commented Apr 15, 2016 at 15:42
  • $\begingroup$ To be sure, for a sensitive enough apparatus you would be able to detect the electric field $\endgroup$
    – jim
    Commented Apr 15, 2016 at 18:11
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When doing electrodynamics, you don't really consider a finite distance at which field lines extend - you consider the behavior of the field as it extends to infinity. In other words, when you have a potential that's dependent upon a distance r from the origin, you take the limit as $$ \lim \phi (\textbf{r})\rightarrow\infty $$ and see what happens (e.g. it should approach zero).

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  • $\begingroup$ so electric field will reach electrons at other ends of chamber? $\endgroup$
    – szufla
    Commented Apr 15, 2016 at 11:35
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Yes, because electric field lines travel at the speed of light in vacuum.However its effect at infinite distance would be negligible, as if field did not reach there at all.

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