The field picture near the wires with current.
Due to the presence of a small tangential component of the electric field strength vector at the surface of the conductor with current, the resulting electric field strength vector E is not perpendicular to the surface of the conductor.
This leads to the appearance of the normal component of the Poynting vector at the surface of the conductor. Consequently part of the transmitted energy is absorbd inside the wires of the transmission line.
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Energy flows in static fields.
Formally, the Poynting vector can also be applied to static electric and magnetic fields.
As an example, we can consider a cylindrical capacitor in a homogeneous magnetic field.
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q |
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S |
E |
H |
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r |
H |
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2 r2l |
The energy continuously circulates inside the capacitor along closed trajectories
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The momentum of the electromagnetic field.
The electromagnetic field inside the cylinder has some mass.
As a result of movement, this mass creates momentum
p meff v |
v c |
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meff V |
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via time |
t c |
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- velocity of light
S s meff v
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The momentum of the electromagnetic field.
W S s l S V c c
If some area was crossed by energy W , we can say that the same area was crossed by the mass with respect to relation
W mc2 Vc2
Thus, the equivalent volume density of electromagnetic matter is
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c3 |
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This matter carries the impulse |
p |
meff v |
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c2 |
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The momentum of the electromagnetic field.
The flow of electromagnetic energy circulating in closed circuits creates the angular momentum:
N v rdV S2 |
rdV |
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V |
c |
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Taking into account the |
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qH |
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S 2 rl |
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expression for the Poynting vector |
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dV 2 rdr |
N qH2 |
r22 r12 |
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2c |
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If the external magnetic field is turned off, the capacitor will start to rotate due to the law of conservation of the angular momentum
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