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Electric Charges (Quick Question)

  1. May 7, 2007 #1
    Can some one please explain to me why charged particles attract neutral ones, yet if you place the numbers into the equation Ep=-kQq/r, it will show you that there is no potential energy between a charged particle and a neutral one, because one of the Q's will be 0. How does this make sense. Also, I read somewhere that protons and electrons do not have any effect on the neutrons. I'm confoosed.
     
  2. jcsd
  3. May 7, 2007 #2

    Doc Al

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    Staff: Mentor

    Are you asking about charged particles attracting neutral particles or neutral objects? (Like a charged rod attracting bits of paper.)
     
  4. May 7, 2007 #3
    Hmm.. I think that equation doesn't apply to almost anything, it only applies to spheres that are uniformly charged.

    anyways, if you bring a charged object near neutral one, what you think would happen to electrons in the neutral object? (remember, they are free to move in the conductors)
     
  5. May 8, 2007 #4

    Mentz114

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    Gold Member

    Usually a charged particle will not atract or repel a neutral one electrically. If you've been told they do, you have been misinformed. Your deduction from the equation is correct for particles.
     
  6. May 8, 2007 #5
    Thanks, I thought particles and objects are the same things.
     
  7. Jun 5, 2007 #6
    k, say you bring two speres (1 charged, one not) close together. Wouldn't the charged object(-) push the electrons to the other end of the sphere, thus making the side of it charged positively, would they then attracts to the charged object? ISn't there a force there? How would you calculate it?

    Also, if you brought a positive(+) charged object near the neutral one instead of negative, would the attraction be weaker, due to the prontons not being able to move, thus adding some positive charge to the same side, some cancelling negative charges from the electrons?
     
  8. Jun 5, 2007 #7

    Doc Al

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    Note that these spheres are objects composed of gazillions of charged particles. Yes, you will get charge separation/polarization. Note that this brings the +charges in the uncharged sphere closer to the charged sphere than the -charges--thus you get an attractive force. How much charge separation depends on the nature of the objects: in a conductor, electrons are free to move; in an insulator, they are bound to the nucleus, but can move somewhat, depending upon the polarizability of the material.

    You get the same thing, only in reverse. Now the electrons in the uncharged sphere move towards the charged sphere, leading to a similar attractive force.
     
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