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Homework Help: Potential due to point charge

  1. Feb 24, 2007 #1
    1. The problem statement, all variables and given/known data
    The electric potential at a distance of 20.5 cm from a very small charged sphere is 33.0 V, with the potential taken to be zero at an infinite distance from the sphere.

    If the sphere is treated as a point charge, what is its charge?

    2. Relevant equations

    [tex] V = \frac {U} {q_{0}} == \frac {1} {4*pi*(8.85*10^{-12})}*\frac {q} {r} [/tex]

    3. The attempt at a solution

    How do you convert 33.0V to the correct units of Q or is it equliv?

    [tex] \frac {1} {4*pi*(8.85*10^{-12})}*\frac {33.0} {0.255} [/tex] ??
  2. jcsd
  3. Feb 25, 2007 #2


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    Staff Emeritus
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    Gold Member

    You don't need to convert your potential into anything, you already have an expression for V, so use it;

    [tex]V = k\cdot\frac{q}{r} \Leftrightarrow q = \frac{V\cdot r}{k}[/tex]

    Also note that [itex]20.5 cm \neq 0.255 m[/itex], its probably just a typo.
  4. Feb 25, 2007 #3
    Thank you, yes that was a typo.
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