Energie gedragen door elektromagnetische golven

The energy density corresponding to electric and magnetic fields of an electromagnetic wave is proportional to the square of the respective field magnitudes.

Thus, the total energy density equals the sum of the energy density of both fields. Using the relation between the fields, the expression for energy density shows that the energy due to the individual fields is equal and total energy density is double the energy density due to an individual field.

Now, consider an area perpendicular to the direction of propogation. The distance traveled and the energy passing through the volume in a small interval due to the wavefront can be determined.

From this, the energy flow per unit area per unit time, or the energy flux, can be obtained.

In general, energy flux is defined as the cross-product of the electric and magnetic fields. This quantity is known as the Poynting vector.

It is directed along the electromagnetic wave propagation, and its magnitude gives the rate of energy flow.