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1. The problem statement, all variables and given/known data

A solid insulating sphere of radius a = 4.9 cm is fixed at the origin of a co-ordinate system as shown. The sphere is uniformly charged with a charge density ρ = -108 μC/m3. Concentric with the sphere is an uncharged spherical conducting shell of inner radius b = 12.8 cm, and outer radius c = 14.8 cm.

1) What is Ex(P), the x-component of the electric field at point P, located a distance d = 34 cm from the origin along the x-axis as shown?

What is V(b), the electric potential at the inner surface of the conducting shell? Define the potential to be zero at infinity.

What is V(a), the electric potential at the outer surface of the insulating sphere? Define the potential to be zero at infinity.

2. Relevant equations

U12=k(q1q2/r12) k=9E9

3. The attempt at a solution

I was able to find the answer to the first question using the equation i gave but when i tried that for 2 and 3 it didnt work and gave the message: "It looks like you have calculated the potential at the inner radius of the shell to be equal to the potential at r = c produced by the insulating sphere by itself. The conducting shell plays a role here. Go back to the definition of the potential to determine the answer."

I don't really understand how the outside uncharged spherical conducting shell can have any effect when it is uncharged. I must be missing something here. Please give input. A diagram is attached.

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# Homework Help: Potential of Concentric Spherical Insulator and Conductor -- Please Help

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