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 .