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Homework Help: Invisible charge?

  1. Jun 15, 2013 #1


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    "Invisible" charge?

    HI all,

    1. The problem statement, all variables and given/known data
    See attached picture. q1 is at equal distance from A or B.
    k = coulomb's constant

    2. Relevant equations

    VA = (k q1 / r)
    VB = (k q1 / r)

    3. The attempt at a solution

    VAB = VA - VB = 0 V

    It seems that the charge becomes invisible in that case, right?

    Attached Files:

  2. jcsd
  3. Jun 15, 2013 #2


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    Staff: Mentor

    The charge is not invisible.

    We have (roughly) the same gravitational potential everywhere on the surface of earth. Is earth invisible? Do you float freely in space?
  4. Jun 16, 2013 #3


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    Gold Member

    That's right but its effect on voltage difference is the same as if there was no charge.
  5. Jun 16, 2013 #4
    Any charge configuration admits equipotential surfaces. The potential difference between any two points on such a surface is zero. Which does not mean there is no charge.
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