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

$$\vec{B}=\frac{\mu_0 r}{A} \frac{dQ}{dt}\vec{e}_\phi$$

(probably this whole thread could have been just a comment and an edit to the previous question)


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