Potential for two semicircular rods

1. The problem statement, all variables and given/known data
Two semicircular rods, one of radius R1 and the other of radius R2 where R2 > R1, are joined by two horizontal, straight rods. The rods carry a charge of lambda coulombs per meter. Calculate the potential at point p at the center of the two semicircles. (P would be the center of the two concentric circles if the rods were full circles)

This configuration looks like a rainbow basically and p is on the ground halfway between each side of the rainbow.


2. Relevant equations
V= KQ/R
V= E*s

3. The attempt at a solution

If I calculate V using the electric field, does the electric field between the two rods cancel so I would just have to use the electric field due to the inner rod? I know the electric fields of the two horizontal rods cancel.
 
Anyone?
 
OK I suppose my real question is, is the electric field at point P

2k(lambda)*(1/R1 + 1/R2)

And then if that is so, to find the potential does the integral go from 0 to R1?
 

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