# Energy and Momentum in Electromagnetic waves

1. Apr 28, 2004

### desibrij_1785

Help me...

A sinusoidal electromagnetic wave from a radio station passes perpendicularly through an open window that has area of .5m^2. At the window, the electic field of the wave has rms value of .02 V/m. How much energy does this wave carry through the window during a 30sec commercial?

2. Apr 28, 2004

### Staff: Mentor

Poynting vector describes energy flow

The rate of energy flow per unit area of an electromagnetic wave is given by the Poynting vector:
$$\vec{S} = \frac{1}{\mu_0} \vec{E} \times \vec{B}$$

The magnitude of the Poynting vector can be shown to be:
$$S = \frac{E^2}{c\mu_0}$$

3. May 3, 2004