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Potential of a Charged Spherical Shell

  1. Apr 5, 2015 #1
    1. The problem statement, all variables and given/known data
    A hollow spherical conductor, carrying a net charge +Q = 47 pC, has inner radius r1 = 5.9 cm and outer radius r2 = 11.9 cm. At the center of the sphere is a point charge +Q/2.

    a. Find the potential at r = 18.0 cm.
    b. Find the potential at r = 10.0 cm.
    c. Find the potential at r = 4.0 cm.
    HW7_4.jpg

    2. Relevant equations
    V= Q/4πε0*r (for potential of a sphere)
    1pC=1.0E-12C ​
    3. The attempt at a solution
    First I converted pC to C, so I get 4.7E-11C. Then I used the equation for potential, so I just substituted the values of r and used the different values of Q depending on whether the potential I need to find is near to Q or to Q/2. (i.e., Q/2 when finding V at 4cm). I'm not sure what charge I should be using or if there are more steps than simply plugging in numbers.
     
  2. jcsd
  3. Apr 5, 2015 #2

    Orodruin

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    You need to sum the potentials from all charges at every r. You must also keep in mind that the formula you have given for the potential from a sphere is only valid outside of the sphere. Do you know what the potential inside the sphere is?
     
  4. Apr 5, 2015 #3
    So I would find the potential outside sphere and also find the potential inside the sphere? The equation for the potential inside the sphere is V=kQ/R, so does the R represent the distance away from the center?
     
  5. Apr 6, 2015 #4

    Orodruin

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    No, if it did there would be no difference to the formula for the potential outside. If you found the formula, there should be a description of what R is in connection to it.
     
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