[[Electrodynamics MOC]]
# Electromagnetic energy density

The **energy density** stored by the [[Electric field|electric]] and [[Magnetic field|magnetic]] fields is given by
$$
\begin{align*}
u = \frac{1}{2}\left( \frac{1}{\mu_{0}}B^2 + \epsilon_{0}E^2 \right) 
\end{align*}
$$
This quantity is required to state conservation of momentum in electrodynamics via [[Poynting's theorem]].


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