Hi. I have no idea how to do this. It's complicated because the length here is a variable. I posted the same question before but there was a little mistake so I am reposting this again. The picture below shows the potential due to ring charge. Please show the full steps of deriving the equation of electrical potential shown in the picture. I have no idea how to start. NOTE: The electric potential of the revolving symmetrical ring electric charge related to the axis z as depicted in the diagram 5.3. It is commonplace to use complete circle integral function in the charge simulation method. If the position (height) of ring electric charge is Z, the radius is R, and the charge density is λ, the electric potential of the point P will be as represented in the next equation. In the equation, l is the distance between the part of the ring charge dθ and P.