Potential for two semicircular rods

[phantom113]

Homework Statement

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.

Homework Equations

V= KQ/R
V= E*s

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.

 

[phantom113]

Anyone?

 

[phantom113]

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?