Electric Potential of charged isolated body.

[ForTheGreater]

Homework Statement

Two equal isolated metallic bodies A & B start with no charge and zero potential. A is given a charge giving B the potential U. B is then Grounded giving A the potential U.

What potential did A have before B was grounded?

Hint: Use symmetry and use potential coefficients.

Homework Equations

V2-V1=int(E,1,2)
V=1/(4*pi*eps) * int(e_density/R dl)

The Attempt at a Solution

Don't know where to start here. The answer includes only U as variable. I think it's a question about relations.

 

[haruspex]

Suppose A started with charge Q, and this led to potential V at A and U at B.
If A had started with charge 2Q instead, what would the two potentials have been?

 

[ForTheGreater]

Suppose A started with charge Q, and this led to potential V at A and U at B.
If A had started with charge 2Q instead, what would the two potentials have been?

2V and 2U.

I should have stated that with no charge both potentials is zero.

I don't see your point. The anser is V_A = U (√ 5 +1)/2

 

[haruspex]

I don't see your point.

It's the first small step. Generalise it as a relationship between the charge placed on one of the objects and the consequent changes to the potentials of each object.
(Encouragingly, the answer you quote is the one I got.)