# Formula Poynting Vector Power density Magnetic field Electric field

## Power density

`$$ \boldsymbol{S} $$`Unit

`$$ $$`

Poynting vector describes the

*energy*passing through a cross-sectional area per unit time. The Poynting vector is thus a power density.The cross-sectional area is spanned by \( \boldsymbol{E} \) and \( \boldsymbol{B} \). The Poynting vector is orthogonal to \( \boldsymbol{E} \) and \( \boldsymbol{B} \).

## Magnetic field

`$$ \class{violet}{\boldsymbol{B}} $$`Unit

`$$ \mathrm{T} $$`

Magnetic flux density determines the strength of the magnetic field and thus the magnitude of the Poynting vector.

## Electric field

`$$ \boldsymbol{E} $$`Unit

`$$ \frac{\mathrm V}{\mathrm m} $$`

The E-field vector indicates the strength of the electric field. The magnitude of the E-field determines the magnitude of the Poynting vector.

## Vacuum permeability

`$$ \mu_0 $$`Unit

`$$ \frac{\mathrm{Vs}}{\mathrm{Am}} = \frac{ \mathrm{kg} \, \mathrm{m} }{ \mathrm{A}^2 \, \mathrm{s}^2 } $$`

The vacuum permeability is a physical constant and has the following experimentally determined value:

`$$ \mu_0 ~=~ 1.256 \, 637 \, 062 \, 12 ~\cdot~ 10^{-6} \, \frac{\mathrm{Vs}}{\mathrm{Am}} $$`