State Ampere's law and Biot-Savart law.

Explanation

Ampere's law : The line integral of the intensity of magnetic induction around a closed path is equal to `mu_(0)` times the total current enclosed in it.
`therefore oint vecB. Vecd l = mu_(0) i.`
Biot-Savart's laws : Biot-Savart's states that the intensity of magnetic induction (dB) due to a small element is directly proportional to the
i) current (i)
ii) length of the element (dl)
iii) sine angle between radius vector (r) and dl and
iv) Inversely proportional to the square of the point from current element.
`therefore dB prop. (i d l sin theta)/(r^(2))`
`dB = (mu_(0))/(4 pi). (i dl sin theta)/(r^(2))`