Poynting's Theorem

#Physics

$\displaystyle \text{d}{t}W=-\text{d}{t}\int {\mathcal{V}} u , \mathrm{d}\tau-\oint{\mathcal{S}}\vec{S}\cdot \mathrm{d}\vec{a}$

• Work done on charges by fields is equal to decrease in energy of the fields plus the energy flowing out of the surface
• $\displaystyle u$ is the electromagnetic field energy density
• $\displaystyle \vec{S}$ is the Poynting vector