In electromagnetism, an Amperian loop is a closed loop that’s used in Ampere’s law to calculate the net current enclosed the surface bounded by the loop. Mathematically, it corresponds to the closed contour in the left-hand side of the Stokes’ theorem.
The Amperian loop has an orientation. Similar to flux integral calculations, our fingers can point in the orientation of the contour. Any current in the direction of our thumb is considered positive, and any current opposite is negative.
Choosing a loop
For the purposes of what I know so far, only a circle is realistically useful, especially for toroidal symmetry.
See also
- Gaussian surface, the divergence theorem analogue