Question

A rod carrying a total charge Q uniformly distributed along its length L (constant λ) **** on the x-axis a distance L from a semi-infinite rod with the same uniform charge density λ as the finite rod as shown in the Figure. What is the magnitude of the net electric field at the point P on the x-axis a distance L from the end of finite rod?

Answer 1

The net electric field at the point P is the superposition of the forces from each of the two rods (finite and semi-infinite) as follows:

where I used λ = Q/L and I used the fact that the point P was a distance 3L from the end of the semi-infinite rod.