**Introduction to Electrodynamics**by

**David J. Griffiths**.

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My problem is that I'm unable to understand how the current has zero $\phi$ component (I have underlined it in the first image)? I do understand cylindrical coordinates, I know cylindrical coordinates involve three components $(r, \phi, z)$ and $\hat{r}$ points radially outwards, $\hat{\phi}$ points perpendicular to $\hat{r}$ and even to $z$ axis.

I fully understand this image (credit: Frobenius)

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But in spite of all these I can't seem to understand how the current have no $\phi$ component, Well, in that toroid we have current going on in circles and really I don't anything more than this.

I tried making some diagrams for understanding it, like these

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I asked some people and they have this to say

There will always be a $\phi$ component of II from the toroid, but if $n=N/L$ is made very large, then the toroid current $I$ can be minimized. This step is really necessary, because it really simplifies things.

Please help me, devise your own method to explain me. I have tried so so hard to understand them but to be honest it seems to me that the things that I have quoted above have no relation to what I asked. Please help me.Theoretically, we can also make the wire as fine as possible. The result is a current per unit length exactly how it is modeled, without any $\phi$ component, with $n=N/L \to ~+\infty$ , and $I \to 0$, and finite current per unit length $K=nI$