Electromagnetic field

Experiment has shown that non zero current flows inside conductor generates magnetic field around conductor

Straight line conductor		Magnetic field is made of circular loops around straight line conductor
Circular loop conductor		Magnetic field is made of circular loops around a point charge on the circle
Coil of N circular loops		Magnetic field is made of eleptic loops run from north pole to south pole

Electromagnetic field's strength

The strength of magnetic field can be calculated by Ampere's law as follow

${\displaystyle B=Li}$

Straight line conductor		${\displaystyle B=Li={\frac {\mu }{2\pi r}}i}$
Circular loop conductor		${\displaystyle B=Li={\frac {\mu }{2r}}i}$
Coil of N circular loops		${\displaystyle B=Li={\frac {N\mu }{l}}i}$