1. The problem statement, all variables and given/known data Two long wires with the same cross section are arranged in air PARALLEL to each other . Assume both have opposite charge densities +λ and -λ. The distance between the axis of the wire is η times larger than the radius(r) of wires cross section . What would be the capacitance of the wires per unit lenth? 2. Relevant equations Electric field of any point between these wires at a distance x from the +λ charged wire is λ/2πε[1/(x)+1/(ηr-x)] 3. The attempt at a solution The problem I am facing is about the limits to be used while integrating Electric field to get the potential . We know that V=-∫Edx (Between some limits) So ∫Edx =λ/2πε[ln(x/ηr-x)] And if I integrate it over 0 to ηr The I will get stuff like ln 0 and ln∞ which are obviously not defined . Some other limits just dont get the right answer which is πε/ ln η .