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Paper and a charged rod

QUESTION:

Can you tell me which one of the following statements best explains why tiny bits of paper are attracted to a charged rubber rod? Now the rubber rod is an insulator, and the paper is also an insulator, since they use it in capacitors it would seem that to attract paper the rubber rod would have to repel electrons in the paper which would leave a surface charge of + then they would attract
Possible answers:
1. Paper is positive material,
2. Paper is negative material,
3. Paper becomes polarised by induction
4. Rubber and paper attract each other
5. Paper acquires a net positive charge by induction


Answer.

The charges in the paper are polarised. Those of similar charge to the excess charge on the rod are repelled and those of opposite charge are attracted. This leaves an area of opposite charge near the rod and so since the paper scraps are so light they can be lifted up by this attraction.

So the last answer is not correct. The charge on the paper remains the same it is just that this charge is distributed differently.

The correct answer is number 3: Paper becomes polarised by induction.

 
 
 
© Keith Gibbs 2011