Potential of a Charged Spherical Shell

[Estefania_8]

Homework Statement

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.

Homework Equations

V= Q/4πε₀*r (for potential of a sphere)
1pC=1.0E-12C​

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.

 

[Orodruin]

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?

 

[Estefania_8]

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?

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?

 

[Orodruin]

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?

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.