# Electrophorus: Why can't we use a magnet in substituion of a charged body to induce the polarization?

Since a magnetic field can induce a current in a coil, moving electrons from one side to another. Why isn't possible to use the same principle in a electrophorus using one magnet instead of charged body?

What's the difference between induction with magnetics and a negatively charged body?

P.S: I'm not asking for clarification about the difference about a magnetic field and a electric filed. Maybe it's related, but my point is that if both can induce charges, why it cannot act as a substitution on a electrophorus?

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The difference is between English and other, more selective laguages, where the electrostatic "induction" is called influence, thus avoiding such questions. Even in portugese its called influencia, look here in the worldreference pages for influence machines: coe.ufrj.br/~acmq/eletrostatica.html – Georg Dec 3 '11 at 22:59
@Georg The question remains the same. And in Portuguese (Brazil) it's not called "influencia" pt.wikipedia.org/wiki/Indução_eletromagnética. Can't see the difference though. Can you post a answer? I would appreciate. (P.S: en.wikipedia.org/wiki/Electromagnetic_induction) – TPH. Dec 4 '11 at 1:57
@Georg the link you have provided doesn't work. Also, I have misspelled it. I actually meant induce, not "induct". – TPH. Dec 4 '11 at 2:08
@Georg Now it's working. But the "influence" usage, at last here, is an exception. "Electrostatic induction" is all over the web. But, I still do not see the difference between influence and induction. Can you point it out for me, please? – TPH. Dec 4 '11 at 5:57

The magnetic field only induces currents when it is changing. In the standard electrophorus, you use a static electric field to induce a charge on one part of the metal, and then you manually drain the charge from another part of the metal. When it's a static magnetic field, nothing happens.

You could make an electrophorus by using a coil attached to a pair of plates, then quickly push a magnet so that it runs by the coil, inducing a current which charges the plates, then (quickly, while the magnet is still moving), disconnect the coil from the plates. This would work to charge the plates, but it isn't an elecrophorus, but a minature dynamo used to charge a capacitor.

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Why nothing happens when it is a static magnetic field? Doesn't positive particles and the negative ones separates? Maybe you meant that there nothing happens with the total amount of charge? Isn't? Now, for clarification, with magnetic induced current (not static) the electrons move to one side, the induced one, but actually not remains on that side after the end of the induction. Therefore, there's no polarization. Am I getting it right? If yes, one more thing: With a induced magnetic current the total charge actually increase or decrease, or it remains the same? Btw: Thanks for the help. – TPH. Dec 4 '11 at 10:34
A static magnetic field does not exert a force on charged particles. For there to be a force from a static magnetic field, the particle must be moving. Per WP: Lorentz force, $\mathbf{F} = q[\mathbf{E} + (\mathbf{v} \times \mathbf{B})]$; note that if $\mathbf{v}$ is 0 then $\mathbf{B}$ contributes nothing. – Kevin Reid Dec 4 '11 at 13:53
@KevinReid OK! Now I see that I'm missing a lot. Mathematically I get it. But It seems like I need to study more before post any questions here, since I cannot understand how a separation can occur without any force. And I just get down-voted for this. Thanks anyway. Your comment was helpful. – TPH. Dec 4 '11 at 20:15
It cannot occur: A static (or, constant) magnetic field does not exert a force on charged particles and does not cause any separation. On the other hand, a constant electric field does exert a force on charged particles, and causes separation. – Kevin Reid Dec 4 '11 at 21:40
+1ed @KevinReid Thanks for your patience. – TPH. Dec 5 '11 at 2:21