State and explain Ampere's law.

Explanation

Statement : The line integral of magnetic field of induction `vecB` around any closed path in free space is equal to `mu_(0)` times the total current flowing through area bounded by the path .
`oint vecB. vec(dl)=mu_(0)I`
Explanation : Consider a long straight conductor in which current 'I' is following. Imagine a closed curved Amperian loop having radius 'r' and length `vec(dl)`. Let `vecB ` be the strength of magnetic field around the conductor.

Then, according to Ampere's circuital law,
`oint vecB.vec(dl) =oint B.dl cos theta`
where `theta` is the angle between `vecB and vec(dl)`.