I need help with the attached exercise. Problem is not that I am not able to do it. You can find the field of an infinite cylinder with Gauss' law and then use that to find the potential difference. My solutions notes however do it in a slightly different way, still arriving at the correct results. They use the expression for the potential of an infinite line: V(r) = −1/(4[itex]\pi[/itex][itex]\epsilon[/itex]0)(2Q/L) ln(r/R0) And simply use that to calculate the potential difference. Can someone explain to me why this would yield the same result?