Poynting Vector?

Question

Need to know what it is (concept + formula) and what its uses are?

Answer 1

It's the energy flux of an electromagnetic wave.

See here...
http://en.wikipedia.org/wiki/Poynting_vector

Answer 2

If in a given volume there is a change in the electro magnetic energy, then that change in energy is equal to the flux of the Poynting vector through the surface bounding the volume under consideration.

In essence, Poynting’ theorem is a direct consequence of the law of conservation of energy.

Answer 3

the Poynting vector can be thought of as representing the energy flux (W/m2) of an electromagnetic field. It is named after its inventor John Henry Poynting. Oliver Heaviside independently co-discovered the Poynting vector. Usually, it is defined as

S = E * H =( 1 / μ0*μr)(E * B)

where E is the electric field, H the magnetic field strength, B the magnetic flux density, μ0 the permeability of vacuum, and μr the dimensionless relative permeability of the surrounding medium. (All bold letters represent vectors.)