# Closed magnetic circuit ( Lorentz force )

## Description

An electromagnet is a type of magnet in which the magnetic field is produced by electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet. For a closed magnetic circuit (no air gap), such as would be found in an electromagnet lifting a piece of iron bridged across its poles, the Lorentz force of the magnetic field can be calculated by the electric current, the length of the of the magnetic circuit and the cross sectional area of the core.

Related formulas## Variables

F | The Lorentz force (N) |

μ | The magnetic permeability of the core material (H/m) |

N | The number of turns (dimensionless) |

I | The electric current (A) |

A | The cross sectional area of the core (m^{2}) |

μ_{0} | magnetic constant |

L | The average length of the magnetic circuit (m) |