# Discussion Forum

## Current Density

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Thomas Eichhorn

November 26, 2012 10:58am UTC

Current Density

Can anyone tell me, why the currenty density is quoted in A and not in A/m^2?

I have a sphere with several layers. Each is made of different material. After I've computed the electric currents, I wanted to evaluate the current density on the different surfaces. When I go to derived values>surface integration and choose the current density, x/y/z-component to be evaluated it is qouted in A. Why is that?

Erik Bornhöft
COMSOL Employee
Germany

November 26, 2012 1:58pm UTC in response to Thomas Eichhorn

Re: Current Density

Dear Thomas,

the "surface integration" will integrate over the specified area. That is why the integral over "A/m^2" will yield to a result in "A". Other example: The integral over "1" will yield to the total area of that surface.

If you want to calculate the average current density on that surface instead, you can use the "average" evaluation function.

--
Hope that helps!

Best regards,
Erik

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Thomas Eichhorn

November 26, 2012 2:25pm UTC in response to Erik Bornhöft

Re: Current Density

Thanks a lot Mr.Bornhöft!

But I have another problem with the same model.
My starting position is an implemented electric current dipole which is place somewhere in the sphere. This yields to the electric currents, I want to compute. But what can I do, if I want to compute the magnetic field??

If I choose for example "Magnetic Fields" or "Magnetic and Electric fields" as my physics and implement the dipole in the same way, the outcome is neither a magnetic field nor an electric field, if i define any initial values or no external sources.

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