# How to calculate the magnetic field for a capacitor?

I found this answer: Magnetic field in a capacitor

But I don't understand some aspects. He says that due to the symmetry we can assume that the magnetic field has the form:

$$\vec{B}=B_\phi(r) \vec{e}_\phi$$

Which seems logical to me. At the end though, the resulting equation is in the z direction. I get how he got to this answer but I don't understand the logic behind it. The magnetic field is only in the ϕ direction so why is it suddenly in the z direction? Thanks!

My guess is that it was a typo. The curl of the magnetic field is along $$z$$, so the magnetic field itself cannot be along $$z$$ as well. The author wanted to write
$$\vec{B}=\frac{\mu_0 r}{A} \frac{dQ}{dt}\vec{e}_\phi$$