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mr_coffee

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A metal sphere of radius 15 cm has a net charge of 2.0 10-8 C.

(a) What is the electric field at the sphere's surface?

7992.7 N/C

(b) If V = 0 at infinity, what is the electric potential at the sphere's surface?

V

(c) At what distance from the sphere's surface has the electric potential decreased by 700 V?

I found part (a) by finding [tex]\delta[/tex] = Q/A; Then using E = [tex]\delta[/tex]/Eo; Which was correct.

But for (b) I Saw [tex]Vf - Vi = -\int E.ds.[/tex]

So Vf- Vi is electric potential. So i tried:

V = -E*d = -(7992.7N/C)(.15) = -1198.905 V but was wrong, any ideas why?