i have been studying electromagnetism on my own and I got a question about an exercise in David Griffiths, Introduction to Electrodynamics book.
So I'm asked to calculate the magnetic field both inside and outside the wire created by a steady current $I$ that flows down a long cylindrical wire of radius $a$ in the $x$ direction.
I know the solution but I don't understand it and was hoping you guys could help me out, By the way we can use the Ampere's Law. One of my confusions is that the direction is going to be circumferential and I don't really understand what this means, also I don't get why it is going to be zero when $s$ is lower than $a$. Any help is appreciated.