Electric Energy Density

${\mu }_e=\frac{1}{2}ϵE^2$ See Chapter 9 Capacitor notes. This is derived from the energy stored of a capacitor, given by

$U=\frac{1}{2}C{V}^2=\frac{1}{2}\frac{ϵA}{d}(Ed{)}^2$

Energy density is then obtained just dividing $U$ by the volume, $V=Ad$ so everything simplifies down to ${\mu }_e=\frac{1}{2}ϵE^2$

Related

• Magnetic Energy Density