Originally Posted by

**braddy** Hi I think I am missing something in the solution of this problem.

I have the final solution of the problem but I get something a little bit different:

**A circular disk of uniform surface integral "RHOs" and radius a lies in the x-y plane with center at (0,0,0). Find the potential PHI(z) along the z axis when the potential is Vo is at the center of the disk, using the potential formula.**

the final answer is:

PHI(z)=(RHOs/2*epsilon0)*[sqrt(a^2+z^2) -z**-a**]+Vo

I found:

PHI(z)=(RHOs/2*epsilon0)*[sqrt(a^2+z^2) -z]+Vo

I dont know how they get the variable a in bold.

Please can someone tell me what I get it wrong.

Thank you.

B