In electrostatics, what is meant by positive charges?

  • #1
I am needing clarification for a concept. I understand that electrons carry a negative charge and that protons carry a positive charge. I also understand that a plastic rod picks up electrons when I rub it with a piece of wool. From the conservation of charge, the piece of wool must have a positive charge. Is this positive carried by protons, or is it a consequence of the loss of some electrons?
 

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  • #2
Dale
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From the conservation of charge, the piece of wool must have a positive charge. Is this positive carried by protons, or is it a consequence of the loss of some electrons?
They are the same thing. An excess of protons is the same as a deficit of electrons.
 
  • #3
Ibix
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Is this positive carried by protons, or is it a consequence of the loss of some electrons?
Both. You aren't adding protons, if that's what you mean, just moving electrons somewhere else.
 
  • #4
sophiecentaur
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Both. You aren't adding protons, if that's what you mean, just moving electrons somewhere else.
The protons in a material are fixed in pretty tight to the atoms - you are unlikely to be able to shift those little devils without a high energy particle beam. To get an object positively charged, you have to take away some electrons. The first few billion would come away fairly easily off a metal.

The net charge imbalance on an object involves only a very small fraction of the total charges (positive and negative) in all the atoms. To strip an electron from every atom in a gram of solid copper, say would involve colossal electric forces (think Inverse Square Law and Atomic distances!!) and any object would just fly apart by repulsion.
 
  • #5
Ibix
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The protons in a material are fixed in pretty tight to the atoms - you are unlikely to be able to shift those little devils without a high energy particle beam. To get an object positively charged, you have to take away some electrons.
Yes - that's what I meant.

OP - your question isn't well phrased. Charged objects are said to carry a charge. Protons always carry a positive charge, electrons always a negative one, and ordinary matter carries either a positive, negative, or no charge depending on whether it's got more protons than electrons or the other way around, or equal numbers. But protons aren't mobile in solids, while electrons can be - so any net charge a lump of matter has is a result of electrons being added or removed.

So the answer to your first option is yes - the positive charge is carried by the protons. And the answer to your second option is also yes - the net positive charge is due to you having removed electrons. I suspect that the latter is what you wanted to know.
 
  • #6
sophiecentaur
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Yes - that's what I meant.
I wasn't disagreeing with you - just amplifying your point. Of course, in a gas / plasma / ions in water, the positive charged ions are free to move so it has to be pointed out that the message only relates strictly to solids.
 
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  • #7
vanhees71
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More precisely it relates to (solid) metals, where the positive ions define the "natural" restframe of the medium, and in this rest frame the conduction electrons make up the current.

This is not true, e.g., in semi-conductors, where rather the holes can make the conduction-charge carriers, and these are positive quasiparticles (though it's again not the positive ions in this case!).

By definition, in a plasma both the positive ions and the electrons move freely and both make up the electric currents (in the local rest frames of the fluid as a whole).
 
  • #8
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I actually less nagtive chrage for
 

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