# Homework Help: Curl of Z-unit vector in spherical coordinates

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1. Dec 6, 2014

### SalcinNossle

1. The problem statement, all variables and given/known data

There is a sphere of magnetic material in a uniform magnetic field $\vec H_0=H_0\vec a_z$,
and after some calculations I got the magnetic moment vector $\vec M_0=M_0\vec a_z$, where $M_0$ is something that isnt important to my question. I am unsure if this magnetic moment vector is correct, as I am running into trouble when I try to figure out the equivalent volume current on the sphere:

$\vec J_{mv}=\nabla\times\vec M_0$,

Is it possible for me to take the curl of a Z-vector, in spherical coordinate system?

Edit: I made a mistake in the title, I meant to take curl of Z, not cross with unit normal of surface of the sphere. Sorry!

Last edited: Dec 6, 2014
2. Dec 6, 2014

### TSny

Hello. Are you asking if it is possible to take the curl of the unit vector $\hat{a}_z$ in spherical coordinates?

If so, the answer is yes. You can do it as an academic exercise, but that would not be the easiest way to get the answer. Note that $\hat{a}_z$ is a constant vector - it is the same vector at all points of space. So, you are taking the curl of a constant vector and the result should be immediate. Or, you can easily see what the result is by taking the curl in Cartesian coordinates rather than spherical coordinates.

If you do want to take the curl in spherical coordinates, then you would want to express $\hat{a}_z$ in terms of the spherical coordinate unit vectors $\hat{a}_r$, $\hat{a}_{\theta}$, and (if necessary) $\hat{a}_{\phi}$.

3. Dec 6, 2014

### SalcinNossle

Thank you! I did take the curl in spherical coordinates for practice, and I got zero! I think it' correct.

4. Dec 6, 2014

### TSny

OK. That's good.