# Clarification on field intensity (electromagnetism)

## Main Question or Discussion Point

Is the intensity of a general electromagnetic wave always the norm of its Poyinting vector?
Or are there other notions of intensity?

## Answers and Replies

Related Classical Physics News on Phys.org
vanhees71
Science Advisor
Gold Member
2019 Award
Since by definition "intensity" is the energy flux per unit time that's right, but usually you have to take also the temporal average. Also see

https://de.wikipedia.org/wiki/Intensität_(Physik)

Note that the energy flux for an em. field (in vacuo) is given by the Poynting vector
$$\vec{I}=\vec{S}=\frac{1}{\mu_0} \vec{E} \times \vec{B}.$$

kent davidge