MP9-2: Magnetic Field from Current Segments

MP9-2: Part F of Magnetic Field inside a very long solenoid (other parts posted separately) (spoiler)

MP9-2: Magnetic Field inside a Very Long Solenoid (spoiler)

MP9-2: Force on Moving Charges in a Magnetic Field

MP9-2: Ampère’s Law Explained

One of the main things to keep in mind here is that it's the symmetry of the closed path you're integrating along that matters, not the amount / consistency of current passing through.

Symmetry lets you bring B out of the integral.

MP9-2: Magnetic field from current segments (spoiler)

MP9-2: Electromagnetic velocity filter (spoiler)