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Homework Help: Electrostatic Problems

  1. Jun 24, 2009 #1
    1. The problem statement, all variables and given/known data

    1)Coulomb's law states that the electric force becomes weaker with increasing distance. Suppose that instead the electric force between two charged particles were independent of distance. In this case, would a charged comb still cause a neutral insulator to become polarized? why or why not? Would a neutral insulator still be attracted to the comb? why or not why?

    2)Two metal spheres are hanging from nylon threads. When you bring the spheres close to each other, you notice that they tend to attract. Is it possible that after the spheres touch, they will cling together? why or why not?

    2. Relevant equations

    3. The attempt at a solution
    Here are my attempts. Please correct me if I'm wrong and elaborate on why I'm right if I'm right.

    1)If the electric forces between two charged particles were independent, would this mean the amount of force will be the same anywhere? If this is the case, the charged comb will cause the neutral insulator to become polarized because there is a electric force acting on it and the insulator will be attracted to the comb.

    2)I don't really get how induced charges work. Are the protons and electrons positioning themselves so that the spheres will be polarized? if they touch, wouldn't charges be transferred to each sphere to neutralize them. If this is true, then they cant cling together. I need someone to explain this to me
  2. jcsd
  3. Jun 24, 2009 #2


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    1) There shouldn't be a force on the insulator. The reason for polarization is because the repulsive force on the like charges, when further away from the comb, is less than the attractive force on the unlike charges closer to the comb. Therefore the insulator becomes polarized. But if the Coulomb's law had no distance factor, the forces would be equal, and there woouldn't be any polarization, and so no attractive force. I hope that's understandable.

    2)I don't get it. are the spheres initially charged? If they are, then if they are equally charged, then after touching they would both be neutral and will not attractive. If there is a difference in charge magnitude, then after touching there would be some charge, and induction will cause the spheres to attract. The question isn't very clear.
  4. Jun 24, 2009 #3
    thanks. i think you answered both my questions
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