#### Note: Electromagnetic fieldEdit

As summarized in previous chapters, electromagnetic field is mathematical abstraction of two projections and , which meets Maxwell equations

and may be represented by field lines defined as

#### Definition: Open field lineEdit

Field line is *open*, when it is not closed in plasma.

#### Definition: Closed field lineEdit

Field line is *closed*, when it is closed in plasma.

#### Theorem: Magnetic field line equationEdit

Lets assume electromagnetic field with field lines. Then

__Proof:__

The theorem results from field line definition directly

which is a vector equation of three scalar equations

and thus may be written