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I already know that a charged polyethylene plastic (done by rubbing it with paper) can be used to attract a cardboard. Now, can I 'charge' the cardboard by touching it with the plastic? Supposedly, the cardboard gets the same charge as the plastic, it would repel the plastic after I charge the plastic again and try to make contact with it.

Of course this is all hypothetical; I've actually tried it already and it doesn't work, thus I concluded that the cardboard cannot be charged this way. Probably because it is not a conductor.

Anyway, my question is, is there some scenario that the opposite happens and the cardboard gets the same charge as the plastic?

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If you made the cardboard conducting. Maybe if it's wet. Maybe if you rub the plastic hard on the cardboard (although this usually requires the right type of momentary bonds). This is too open ended--- the "some scenario" is vague. Are you asking "how can I transfer charge from plastic to cardboard efficiently?"? – Ron Maimon Jul 26 '12 at 4:09
Yes, that's what I want to know. – Dystopian Jul 26 '12 at 6:20

2 Answers 2

The cardboard and the plastic become oppositely charged by rubbing. At first approximation, they are both insulators, so the charge can't go anywhere and stays on their surface. They attract each other due to the opposite charges.

If you touch them together, some of these charges will be able to jump back to the other object, effectively discharging the objects. As a result, the attractive force will be reduced.

No, you can't somehow make them both be charged with the same polarity. Think about it. That would require a net imbalance in charge taking the two objects as a whole. If they were initially discharged, where is this net charge supposed to come from? All you can do by rubbing is move some charges from one object to the other.

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As to your question: whether you can do it or not, then the answer is no.

Because, for charge to just simply transfer between two bodies, they must be conductors (because they have low resistance and allow electrons to be easily transferred and redistributed) now since neither the plastic, nor the cardboard is conducting they cannot distribute their electrons. Even if they had been conducting it would not have been possible because then neither of them could be charged simply by charging. If just cardboard was conducting, then the resistance of plastic would not allow redistribution and if plastic was conducting it wouldn't get charged in the first place.

Although if the cardboard was somehow made conducting, then by induction it would be possible to charge the cardboard from the plastic, but by touching it is simply not possible.

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I disagree with your statement that both bodies need to be conductors. What about a charged glass rod (nonconducting) touching a electroscope (foil leaves inside a container). If the charge doesn't transfer, then the leaves wouldn't separate. – LDC3 Mar 27 '14 at 3:47
My statement seems to be misleading, I have not said both need to be conductors, in my complete answer I have simply said if they are both non conducting then charge would not distribute. Please read once more and object again if there is something wrong. Thank you for the comment. – Rijul Gupta Apr 7 '14 at 3:26
This is not your statement? "Because, for charge to just simply transfer between two bodies, they must be conductors (because they have low resistance and allow electrons to be easily transferred and redistributed)" – LDC3 Apr 7 '14 at 3:36
I think due to my misplacement of punctuations what I was trying to say was altered into something else. What I meant to say was that in my complete answer I have not said that they both need to be conductors. I have however written that extremely misleading opening statement on which I believe you are correctly pointing out the mistake. But that is only in that statement. – Rijul Gupta Apr 7 '14 at 16:33
Having recognized that your answer can be improved, why not improve it? – The Photon Dec 31 '14 at 20:22

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