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Electric field of a dipole
Posted Aug 27, 2012, 8:19 a.m. EDT 2 Replies
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Dear Comsol Users
For learning reasons, I have calculated the classic electric field of a 2d dipole. Maybe it is useful for other to know how i did it.
First, I defined two solid circles, for which I wanted to assign a surface charge density of +q/m^2 and -q/m^2. However, this was not possible until I defined an area, where the circles where placed in. So I placed said charges on either circle, and put the enclosing square to zero potential. I thought I could now solve the electrostatic problem, but I received an error message telling me that I need to assign relative permittivity of the circles. I am not interested in the field with in the charges (whatever that might look like) so I performed a geometrical operation being to subtract the circle areas of the surrounding square area. Then I assigned a relative permittivity of 1 to the square area, making it essentially vacuum.
Now I could solve the electrostatic problem and plot the electric potential together with the electric field (see attached figure).
picturepush.com/public/9074172
I would like to ask if this is the recommended way of doing these kind of basic problems. One thing I wonder about is how I can change the plotting of the electric field such that the arrows do not reach into the circles (where there is essentially "nothing"). How do I do that? I tried setting the arrow base to tail, but then they just reach into the other circle.
Thanks for comments.
For learning reasons, I have calculated the classic electric field of a 2d dipole. Maybe it is useful for other to know how i did it.
First, I defined two solid circles, for which I wanted to assign a surface charge density of +q/m^2 and -q/m^2. However, this was not possible until I defined an area, where the circles where placed in. So I placed said charges on either circle, and put the enclosing square to zero potential. I thought I could now solve the electrostatic problem, but I received an error message telling me that I need to assign relative permittivity of the circles. I am not interested in the field with in the charges (whatever that might look like) so I performed a geometrical operation being to subtract the circle areas of the surrounding square area. Then I assigned a relative permittivity of 1 to the square area, making it essentially vacuum.
Now I could solve the electrostatic problem and plot the electric potential together with the electric field (see attached figure).
picturepush.com/public/9074172
I would like to ask if this is the recommended way of doing these kind of basic problems. One thing I wonder about is how I can change the plotting of the electric field such that the arrows do not reach into the circles (where there is essentially "nothing"). How do I do that? I tried setting the arrow base to tail, but then they just reach into the other circle.
Thanks for comments.
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2 Replies Last Post Aug 6, 2016, 10:33 a.m. EDT
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Posted:
1 decade ago
Martin,
exercises like this are an excellent way to start learning COMSOL and go ahead to more complex problems. This way you can check the match between the results and the theoretical prediction. I would recommend this approach to all newcomers. Start simple instead of trying to put all multiphysics complexity into your first modeling attempts.
Regarding the arrows you might consider replacing them by streamlines. The magnitude of the field is already coded by the color map, the streamlines provide the direction information, so arrow length is a bit redundant.
Cheers
Edgar
exercises like this are an excellent way to start learning COMSOL and go ahead to more complex problems. This way you can check the match between the results and the theoretical prediction. I would recommend this approach to all newcomers. Start simple instead of trying to put all multiphysics complexity into your first modeling attempts.
Regarding the arrows you might consider replacing them by streamlines. The magnitude of the field is already coded by the color map, the streamlines provide the direction information, so arrow length is a bit redundant.
Cheers
Edgar
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Posted:
8 years ago
Marin
Could you possibly send me the setup file that you used? I'm struggling with something similar and want to compare it to what you have done.
Could you possibly send me the setup file that you used? I'm struggling with something similar and want to compare it to what you have done.