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Homework Help: Electrostatics: Charging a sphere by induction

  1. Jan 27, 2017 #1
    1. The problem statement, all variables and given/known data

    this is a theoretical question.please consider the situation as follows:
    we are charging a metallic sphere using induction phenomenon with the help of a postively charged metallic rod and while on grounding the electrons flow from the ground to the sphere rather than sphere to ground, why?
    2. Relevant equations

    while charging by induction, the part of the material being induced near to the inducing material gets opposite charge of the inducing material and the other half which is away gets opposite polarity which is same as that of the inducing material's polarity.
    3. The attempt at a solution
    lets say when we bring a negatively charged plastic rod to an uncharged metallic sphere, the part nearer to the inducing material gets positive charge and the other half is negatively charged.on grounding the electrons flows from the sphere to the earth and now the sphere as a whole becomes positively charged. but in the aforementioned case, why does the electron flows from ground to the sphere? what happens in the two cases? please explain.
  2. jcsd
  3. Jan 27, 2017 #2


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    Ground is an infinite source (supply) of charge. When the neutral sphere is grounded, ground either absorbs or supplies electrons depending on the incident field.

    If you took a positively charged object near the sphere, it will attract electrons on the sphere and the charges will distribute on the sphere such that the net field inside the sphere is zero. Since the incident field is from +vely charged object, electrons will be attracted from the ground on the sphere. These attracted electrons will neutralize the positive induced charges and the sphere will now have only negative induced charges.

    If you disconnected the sphere from the ground, the sphere will have a net negative charge.

    So, if the incident field is from +ve charge, electrons will flow from ground to sphere and if the incident field is from -ve charge, electroms will flow from sphere to ground.
  4. Jan 27, 2017 #3
    Thanks.It helped me :)
  5. Jan 27, 2017 #4


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    Well, it looks like I'm going to get a warning soon for providing direct answers in the HH section..?:)
    It would be better if you posted such conceptual questions in general physics or classical physics forums..
    You're welcome!
    Some mentor or SA will come with an even better explanation (and a warning for me:-p)..
  6. Jan 28, 2017 #5
    oh is it? yup i will do it in the future. *posting conceptual questions in classic physics forum. instruction noted.* :)
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