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Why do we consider induction a way of charging?

  1. Apr 16, 2014 #1
    I get that by getting a charged object near an uncharged one, charges of the opposite sign are induced on the surface, but, since the total charge of the whole object is still zero (because electrons move inside the conductor and can't escape because surroundings insulate it) , the object as a whole can't be considered charged, only the surface, so why would we call induction a means of charging while the net charge of the object doesn't change?
  2. jcsd
  3. Apr 16, 2014 #2
    Imagine inducing a charge difference on a long rod. One end is positive, the other negative. Now cut the rod in half. Now you have two separate objects, each with a net charge.

    This is what we mean by "charging by induction". You induce a charge across an object, then cut the connection between the charged ends.
  4. Apr 16, 2014 #3
    so if i didn't cut the object, then i haven't charged it because the net charge would remain zero right?

    Thank you :)
  5. Apr 17, 2014 #4

    Philip Wood

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    Gold Member

    I'd add to axemaster's reply that you don't necessarily have to cut the object to be charged in half, to isolate net charge. Suppose the object to be charged is a conductor, and that you hold it near a negatively charged object, N. Then free electrons in the conductor will be repelled towards the parts of the conductor furthest from N. If you now TOUCH the object, electrons can be repelled even further from N - on to YOU, and probably via you to the ground. The conductor now has a positive charge. Let go of it, THEN remove N, and the conductor will be left with an overall positive charge.

    The same works, making necessary changes to the explanation, for charging a conductor negatively using an external positive object.

    A better explanation of what goes on in each case uses the idea of potential.
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