Electromagnet

For a coil of N circular loops made from straight line conductor

${\displaystyle B=LI={\frac {N\mu }{l}}I}$

Permanent Electromagnet

Permanent Electromagnet Field		${\displaystyle H={\frac {B}{\mu }}={\frac {\phi }{N\mu }}}$
Vector equations		${\displaystyle \nabla \cdot E={\frac {\rho }{\epsilon }}}$ ${\displaystyle \nabla \times E=-{\frac {\partial }{\partial t}}B}$ ${\displaystyle \nabla \cdot B=0}$ ${\displaystyle \nabla \times H=J+{\frac {\partial }{\partial t}}B}$

Subject classification: this is a physics resource.

Subject classification: this is an engineering resource.