# Physics Using Geometric Algebra/Relativistic Classical Mechanics/The electromagnetic field

< Physics Using Geometric AlgebraThe electromagnetic field is defined in terms of the electric and magnetic fields as

which can be derived from a paravector potential as

where:

and

## Lorenz gaugeEdit

The Lorenz gauge (without t) is expressed as

The electromagnetic field is still invariant under a gauge transformation

where is a scalar function subject to the following condition

## Maxwell EquationsEdit

The Maxwell equations can be expressed in a single equation

where the current is

Decomposing in parts we have

- Real scalar: Gauss's Law
- Real vector: Ampere's Law
- Imaginary scalar: No magnetic monopoles
- Imaginary vector: Faraday's law of induction

### Electromagnetic LagrangianEdit

The electromagnetic Lagrangian that gives the Maxwell equations is

### Energy density and Poynting vectorEdit

The energy density and Poynting vector can be extracted from

where energy density is

and the Poynting vector is

## Lorentz ForceEdit

The electromagnetic field plays the role of a spacetime rotation with

The Lorentz force equation becomes

and the Lorentz force in spinor form is

### Lorentz Force LagrangianEdit

The Lagrangian that gives the Lorentz Force is

## Plane electromagnetic wavesEdit

The propagation paravector is defined as

which is a null paravector that can be written in terms of the unit vector as

A vector potential that gives origin to a polarization|circularly polarized plane wave of left *helicity* is

where the phase is

and is defined to be perpendicular to the propagation vector . This paravector potential obeys the Lorenz gauge condition. The right helicity is obtained with the opposite sign of the phase

The electromagnetic field of this paravector potential is calculated as

which is nilpotent