## College Physics (4th Edition)

$\frac{1}{2}\epsilon_0~E^2 = \frac{1}{2~\mu_0}~B^2$ In an EM wave traveling in a vacuum, the electric and magnetic energy densities are equal.
We can show that the electric and magnetic energy densities are equal. $\frac{1}{2}\epsilon_0~E^2 = \frac{1}{2}\epsilon_0~(c~B)^2$ $\frac{1}{2}\epsilon_0~E^2 = \frac{1}{2}\epsilon_0~c^2~B^2$ $\frac{1}{2}\epsilon_0~E^2 = \frac{1}{2}\epsilon_0~(\frac{1}{\sqrt{\epsilon_0~\mu_0}})^2~B^2$ $\frac{1}{2}\epsilon_0~E^2 = \frac{1}{2}\epsilon_0~(\frac{1}{\epsilon_0~\mu_0})~B^2$ $\frac{1}{2}\epsilon_0~E^2 = \frac{1}{2~\mu_0}~B^2$