So i have a thin circular ring laying at the XoY plane, inner radius of the ring is a, outer is b, density of electricity is given by expression ρ=ρ0*b/r , where ρ0 is a constant and r ∈ (a,b). I have to find a potential of the point P with coordinates (0,0,z). I tried to do it two ways, but both of them seem wrong. Firstly, i tried to first find E and then V since V=∫E*dl , but i ended up with E=ρ0*b*z/2ξ0∫dr/(z2+r2)3/2 , this seems wrong to me since in every other example i end up with, at most, integral with substitution, which this one isn't. The other way i tried to do it is, since potential of the single contour gives the value of the potential dV=dQ/4πξ0r potential of the ring in this example would be V=ρ0b*ln(b/a)/2ε0 which makes no sense since there's no z in the solution, which would mean that distance between point and ring doesn't matter, which means that both of these are probably wrong.