# Electric potential at the outer surface of the insulating sphere?

1. Jan 29, 2013

### bodaciousbob

1.A solid insulating sphere of radius a = 3.6 cm is fixed at the origin of a co-ordinate system as shown. The sphere is uniformly charged with a charge density ρ = -218.0 μC/m3. Concentric with the sphere is an uncharged spherical conducting shell of inner radius b = 10.9 cm, and outer radius c = 12.9 cm.

http://imgur.com/R4vpBTr

1)
What is V(a), the electric potential at the outer surface of the insulating sphere? Define the potential to be zero at infinity.

2)
What is V(c) - V(a), the potentital differnece between the outer surface of the conductor and the outer surface of the insulator?

2. Relevant equations

ΔV(a->b) = ∫E.dA

3. I have so many miscellaneous pieces of paper scattered around my room, with chicken scratch on them, as I have been trying to many techniques for the last 3 hours. I just CAN'T get it - so I beg you - someone out there in internet land.. Can you PLEASE give me detailed instructions and walk me through this problem? There are 4 other parts to it, but by SOME miracle I have figured those out... Please?!?!!

2. Jan 29, 2013

### SammyS

Staff Emeritus

Hello bodaciousbob. Welcome to PF !

Have you calculated the total charge on the insulating sphere?

What is the charge on the inner surface of the conducting spherical shell?

What is the charge on the outer surface of the conducting spherical shell?

Start at infinity and find the potential V(c), then V(b), and then V(a) .

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