Explain Biot savarts law ?

We know that electric current or moving charges are source of magnetic field

A Small current carrying conductor of length dl (length element ) carrying current I is a elementary source of magnetic field .The force on another similar conductor can be expressed conveniently in terms of magnetic field dB due to the first
The dependence of magnetic field dB on current I ,on size and orientation of the length element dl and on distance r was first guessed by Biot and savart
The magnitude of the magnetic field dB at a distance r from a current element dl carrying current I is found to be proportional to I ,to the length dl and inversely proportional to the square of the distance |r|
The direction of the magnetic Field is perpendicular to the line element dl as well as radius r
Mathematically, Field dB is written as

Here (μ0/4π) is the proportionality constant such that μ0/4π=10-7 Tesla Meter/Ampere(Tm/A)