Originally Posted by

**JohnDoe** Yes thanks for your help but I am stuck after these step, I cannot find the integral I might be doing something wrong here is my work:

$\displaystyle \frac{{\sigma 2\pi }}{{4\pi {\varepsilon _0}\sqrt 2 }}\int\limits_0^{\sqrt 2 h} {\frac{{\tau d\tau }}{{\sqrt {{\tau ^2} + {h^2} - \sqrt 2 h\tau } }}} \\

{\tau ^2} + {h^2} - \sqrt 2 h\tau = {(\tau - \frac{h}{{\sqrt 2 }})^2} + \frac{{{h^2}}}{2}\\

u = (\tau - \frac{h}{{\sqrt 2 }})\\

\frac{\sigma }{{\pi {\varepsilon _0}2\sqrt 2 }}\int\limits_a^b {\frac{{u + \frac{h}{{\sqrt 2 }}du}}{{\sqrt {{u^2} + \frac{{{h^2}}}{2}} }}} \\$