An experiment is conducted to determine the uniform linear charge density \(\lambda\) of a very long, thin, positively charged wire. The electric potential \(V\) is measured at various radial distances \(r\) from the wire, with the reference potential defined such that \(V = 0\) at a fixed radial distance \(r_0\). Which of the following quantities should be plotted on the vertical and horizontal axes to produce a straight line, and what is the slope of that line in terms of \(\lambda\) and fundamental constants?