Electrodynamics and the Poynting theorem

[AHSAN MUJTABA]

Homework Statement

In static fields, why there exists a field momentum? And if it exists then what's the meaning of it?

Relevant Equations

$S=\frac{1}{\mu_o}(\vec E\times\vec B)$

In my opinion the field momentum is the field's intrinsic momentum which it will give to charges(if any present)...

 

[anuttarasammyak]

Hi. Feynman shows us an interesting example of a point charge sitting near the center of a bar magnet, as shown in Fig. 27–6. Here rotating Poynting vector generates EM field angular momentum. I will explain it.

Let us prepare the system by carrying the charge from infinite distance to the center where the magnetic bar is laid. Lorentz force jams the charge to come to the center by deflection so we apply force on charge sideway. Momentum is transferred to EM field. Thus accumulated momentum in EM field generates the angular momentum.

So it shows that Poynting vector is applicable in static EM field as well as cases of circuit currents and EM waves.

 

[AHSAN MUJTABA]

Thanks it's very deep and helped a lot.