Chapter-4|Moving Charges and Magnetism| NCERT 12th Physics:
Magnetic Field Due to a Current Element: Biot-Savart's Law:
Biot-Savart's law is an experimental law predicted by Biot and Savart. This law deals with the magnetic field induction at a point due to a small current element.
Note: Since, only dl have no direction, So we consider idl(current element) in the direction of current.
(I) Right Hand Palm Rule: Place the thumb of your right hand along the direction of current and curl your fingers, The direction in which your finger curl, gives the direction of magnetic field at that point.
(II) Screw Rule: Place the screw in the direction of current and tight it, Where screw turn gives direction of magnetic field.