Charge Q uniformly spread through the ring of radius a. Find the work done to bring point charge q from the center of ring to infinity along the axis through the center of ring. From a previous problem I calculated E=kQz/(z^2+a^2)^1.5 I then tried to apply the formula W=eo/2[tex]\intE^2 dz[/tex] integrating from 0 to infinity. As a result I got -Q^2/(1024a^3). However the professor on my paper just put an x on it, indicating that it was wrong & then wrote down use the formula W=q(Vo-Vinfinity). So my question is, can I not apply the formula I used for the equation? If not, why?