# Discussion Forum

## 2D Circle around 3D sphere

Hello,

I have a 3D sphere of radius 10mm at potential +1000V. I would like to plot the potential across a circular arc of radius 20mm around the sphere, in the z plane. How can I do so? I've attached an image to show what I mean. I am a relatively new user and would appreciate any help I can get.

Kind regards, Anwesha

3 Replies Last Post Apr 17, 2021, 5:28 PM EDT

Posted: 4 weeks ago
1. Are you having trouble setting up the geometry, selecting the physics, specifying the boundary conditions, defining the mesh, preparing/post-processing of the computed results, or??
2. You only mentioned one potential boundary condition. Is this sphere in free space? If so, we have spherical symmetry and the potential is simply proportional to 1/r, for r>10mm. Thus, if the potential is 1000V at r=10mm, then it is 500V at r=20mm.
3. Ok, so since the answer is already known, you presumably have a purpose in preparing a model anyway? Well, if that purpose is to gain practice/experience in using the code, I suggest you take a look at the tutorial videos provided on-line and also work through (step by step, don't skip ahead) some of the examples available to you in the Comsol application library. See https://www.comsol.com/learning-center .

Posted: 3 weeks ago

Thank you for your response, I appreciate it. The sphere is in free space. I have made the geometry. I'm having trouble evaluating the potential along the arc described. I assume that would be part of post-processing/ results.