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If Electricity and magnetism are the same viewed from a different reference frame (they are the same force as unified by maxwell) then is electricity medium dependant? I came to this question when trying some experiment with two wires close to each other where I place between them non-conductor mediums such as: paper, wood, plastic... And I see some difference. So is the electrostatic force medium dependant? That is, if I have a charge Q1, and Q2, they will attract/repulse each other (F=k.Q1.Q2/r²) based on the medium where they are separated? If so, does it have to do with density, what is the general formula?

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$k$ is normally written as $\frac 1{4\pi\epsilon}$, where $\epsilon$ is the electrical permittivity. This is where the dependence on the medium comes from. It's not dependent on density per se, but how easily the electrons in the material will move in response to the original electromagnetic field.

You might also want to look into dielectrics, where we use this phenomena to our advantage in order to build capacitors and other things.

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  • $\begingroup$ I'm not talking about how easily the electrons in the material will move but how for example an electron and a positron will attract based on the medium. $\endgroup$ Oct 23 '13 at 12:30
  • $\begingroup$ @MyFavouritePhysicistIsNewtax that's what this is: electrons in the intermediate medium are just the reason that this is dependent on medium. The force between the electron and positron will change because $k$ will change, and this is why. If you had a medium whose electrons and atoms didn't move at all in response to an electromagnetic field, then it would behave like a vacuum as far as electromagnetic forces are concerned. $\endgroup$ Oct 23 '13 at 12:33
  • $\begingroup$ Can you do an example please with a paper and a piece of wood? Please... $\endgroup$ Oct 23 '13 at 12:34

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