Visualizing the charge distribution in COMSOL

[feynman1]

How to visualize charge distributions in COMSOL, like showing + or - charges on a surface or a bulk in postprocessing?

 

[DrClaude]

Make a surface plot of the space charge density (es.rhoq).

 

[feynman1]

Make a surface plot of the space charge density (es.rhoq).

Thanks. That's a continuous distribution. What if I want to show discrete +/- charges?

 

[DrClaude]

Thanks. That's a continuous distribution. What if I want to show discrete +/- charges?

There are no such things as discrete charges in the equations being solved, only a charge density.

 

[feynman1]

There are no such things as discrete charges in the equations being solved, only a charge density.

Right. So I assume there's no such feature of visualizing as point charges. Point charges look more intuitive than surface distributions.

 

[feynman1]

Is there a feature of showing induced bound charges?

 

[DrClaude]

Is there a feature of showing induced bound charges?

I dint understand. Do you mean polarization of a dielectric?

 

[feynman1]

I dint understand. Do you mean polarization of a dielectric?

Yes, showing bound charges of a dielectric, caused by polarization.

 

[sophiecentaur]

How to visualize charge distributions in COMSOL, like showing + or - charges on a surface or a bulk in postprocessing?

Is the purpose of this for your internal 'understanding' or is it for the purpose of presenting ideas to others? I could see that a graphic of +and - charges could be familiar for people who are not well informed on the topic but why, as you are clearly familiar, would you want to go for a dumbed-down presentation? Presenting charge density as areas with random + or - signs scattered around could actually end up in a mess of symbols - if you actually want a hint of the quantitative situation. Just try it yourself, putting signs on a diagram, by hand. Is the result satisfactory?

 

[feynman1]

Is the purpose of this for your internal 'understanding' or is it for the purpose of presenting ideas to others? I could see that a graphic of +and - charges could be familiar for people who are not well informed on the topic but why, as you are clearly familiar, would you want to go for a dumbed-down presentation? Presenting charge density as areas with random + or - signs scattered around could actually end up in a mess of symbols - if you actually want a hint of the quantitative situation. Just try it yourself, putting signs on a diagram, by hand. Is the result satisfactory?

Kind of both. Would be nicer to show them in the simulation directly, without myself plotting them.

 

[sophiecentaur]

without myself plotting them.

Yes - of course. But you can see the result for yourself with just one example. Perhaps, rather than spending effort on producing an inferior display system, you could work on a way to explain what the available charge distribution display shows. It's clearly so much more informative that I'm sure you could convince even the most reactionary audience.

 

[DrClaude]

Yes, showing bound charges of a dielectric, caused by polarization.

You can plot the polarization of the material.

To add to what @sophiecentaur said, it would be could for you to learn to interpret the results by looking only at the charge density or the polarization. Using + and - charges may be good for pedagogical purposes (I do use that when I teach), but you'll go farther by being able to lose those training wheels!

Remember also that the actual discrete charges are electrons and ions. Any accurate representation of the charges would include so many of them as to lead back to what you see using a surface plot...

 

[feynman1]

You can plot the polarization of the material.

To add to what @sophiecentaur said, it would be could for you to learn to interpret the results by looking only at the charge density or the polarization. Using + and - charges may be good for pedagogical purposes (I do use that when I teach), but you'll go farther by being able to lose those training wheels!

Remember also that the actual discrete charges are electrons and ions. Any accurate representation of the charges would include so many of them as to lead back to what you see using a surface plot...

yes, one can plot polarization. nice to plot a finite number of +- charges to represent a surface distribution, if possible.