Poynting Vector and Light Intensity

The Poynting vector describes the energy flux of an electromagnetic wave. It tells how much energy passes through a unit area in a unit time at a specific moment. For a plane electromagnetic wave moving along the x-axis, the energy flux depends on the peak electric field E0 and the peak magnetic field B0.

When a capacitor is connected to an alternating current, the direction of the electric field between the plates changes with time, which induces a varying magnetic field.

The energy flow given by the Poynting vector is parallel to the plate. It varies rapidly with time.

Taking the time average of the Poynting vector gives the wave'...