Poynting vector

yannick^

I have a question about the Poynting vector:

mit.edu/8.02t/www/materials/StudyGuide/guide13.pdf (page 44/51)

What is the physical interpretation of "S points radially inward". That seems kinda weird. Energy flows to the center?

cheers

Creator

Couldn't find your exact page on the link....but yes, seems unusual but that is typical for Poynting vector...say, of a coil or capacitor being charged....the energy flows orthogonally into it from the surrounding space otside the coil.

Creator

Domenicaccio

Yes.

It's not so weird after all: while being charged, the capacitor is storing energy in the form of the electrical field which is being "built" in the dielectric material inside it. Since the Poynting vector represents a flow of electromagnetic energy, it makes sense that during charging it will point towards the inside of the capacitor, and during discharging it will point outwards. In a stable condition of the capacitor, the Poyting vector will be null.