# Clarification on field intensity (electromagnetism)

• kent davidge
In summary, field intensity or electric field strength is a measure of the strength of an electric field at a specific point in space. It is calculated by dividing the force acting on a charge by the magnitude of the charge and can also be expressed using the equation E = kQ/r^2. The SI unit for field intensity is volts per meter (V/m), but it can also be measured in newtons per coulomb (N/C) or teslas (T). The stronger the field intensity, the greater the force exerted on objects in its presence, potentially causing them to move or change shape.

#### kent davidge

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

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