Poynting Vector: "S Points Radially Inward" Explained

[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.