Ampere's loop law is used to find

CONCEPT:

Ampere's law

• The circulation ∮ B.dl of the resultant magnetic field along a closed, plane curve is equal to μ0 times the total current crossing the area bounded by the closed curve provided the electric field inside the loop remains constant.

⇒ ∮ B.dl = μ0I

where B is the magnetic field at the length element dl of the loop. I is the sum of all currents inside the loop.

• The sign convention is decided by the right-hand thumb rule.
• Since the loop is clockwise, curl your right-hand fingers along the loop, and the thumb will give the positive direction of current (inside the plane of the paper). Thus i1 and i2 are taken as positive, while i3 is taken as negative. Here i4 and i5 are ignored since they are outside the loop.
• B is the net magnetic field on the loop element.

EXPLANATION:

According to Ampere's law

⇒ ∮ B.dl = μ0I

The equation can be used to determine

• the magnetic field on an assumed Ampere's loop.
• the current flowing through a medium.

Therefore option 1 is correct.