Electromagnet

It was discover by Ampere that when electric conductor conducts current it will generate magnetic field of field intensity

${\displaystyle B=LI}$

Confirguration

For a straight line conductor		${\displaystyle B=LI={\frac {\mu }{2\pi r}}I}$
For a circular loop made from straight line conductor		${\displaystyle B=LI={\frac {\mu }{2r}}I}$
For a coil of N circular loops made from straight line conductor		${\displaystyle B=LI={\frac {N\mu }{l}}I}$