Magnetic Dipole
Every current carrying loop is a magnetic dipole. It has two poles south( S) and north( N).
This is similar to a bar magnet. Each magnetic dipole has some magnetic moment( M). The magnitude of M is, | M | = NiA
where, N = number of turns in the loop, i = current in the loop and A = area of cross-section of the loop.
The current carrying loop behaves as a small magnetic dipole placed along the axis one face of the loop behaves as north pole while the other face of loop behaves as south pole.
Ampere’ s Circuital Law
The line integral of magnetic field induction B around any closed path in vacuum is equal to 110 times the total current threading the closed path, i. e.,
where B is the magnetic field, dl is small element, μ o is the absolute permeability of free space and I is the current.
Ampere’ s circuital law holds good for a closed path of any size and shape around a current carrying conductor because the relation is independent of distance form conductor.