Poynting Vector Direction Confusion

In summary, the Poynting vector of a current carrying wire that is being heated via resistance (Joule heating), has a Poynting vector pointing radially inward. The E field is parallel to the wire, B field is circumferential with the right hand rule.
  • #36
BruceW said:
I see. That's because the resistance of the wire is negligible compared to the resistor at the end. The original question was about the power loss in a wire due only to the Ohmic resistance of the wire. That's why we've been talking about the power going into the wire.

As I said on several occasions, no one is disputing that the Poynting vector points into the wire's axis from its surface. And that's why I said we're probably just confusing the OP since all he/she was interested in was why the Poynting vector pointed towards the axis rather than from the axis to the surface.

I just contested van's assertion that the Poynting vector is the same outside as in. And I have shown that it isn't, even for the case of a dc current in the (inner) wire. It points in the direction of the dc current. Which is the direction of energy travel.
 
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  • #37
vanhees71 said:
Anyway, after all we agree that the fields in the free space between the inner and the outer conductor are responsible for the energy transport from the source ("battery") at the one end to the other.

Exactly. And that's the way the Poynting vector points. From the battery to the load. Not radially.
 
  • #38
If you short the far end instead of applying the resistor the numbers wold be less dramatic: for the same 10V battery, i ~ 100A, j ~ 1.9e8, inner E ~ 3.2V/m, outer E same as before = 1.1e4 (near the battery). The outer/inner ratio is still 34000:1.
 
  • #39
rude man said:
Exactly. And that's the way the Poynting vector points. From the battery to the load. Not radially.

Ok, I see it was a bad idea to take as an example the single wire, where the Pointing vector is indeed radial everywhere :-(.
 
  • #40
vanhees71 said:
Ok, I see it was a bad idea to take as an example the single wire, where the Pointing vector is indeed radial everywhere :-(.

Only in a nonexistent, isolated wire. Any single wire is still part of a circuit, where the Poynting vector points mostly in the direction of current.
 
<h2>1. What is the Poynting vector and how is it related to direction confusion?</h2><p>The Poynting vector is a mathematical concept that represents the direction and magnitude of electromagnetic energy flow. Direction confusion refers to the difficulty in determining the direction of energy flow in certain situations, such as when there are multiple sources of electromagnetic radiation.</p><h2>2. How does direction confusion affect scientific research?</h2><p>Direction confusion can lead to incorrect interpretations of experimental results and can hinder the progress of scientific research. It is important for scientists to carefully consider the direction of energy flow when conducting experiments and analyzing data.</p><h2>3. What factors contribute to direction confusion in the Poynting vector?</h2><p>Direction confusion can be caused by factors such as the presence of multiple sources of electromagnetic radiation, reflections and refractions of radiation, and the orientation of the observer relative to the sources.</p><h2>4. How can direction confusion be minimized in scientific experiments?</h2><p>To minimize direction confusion, scientists can carefully design their experiments to control for the factors that contribute to it. This may include using shielding to block out unwanted radiation sources or carefully positioning the observer relative to the sources.</p><h2>5. Are there any real-world applications of the Poynting vector and direction confusion?</h2><p>Yes, the Poynting vector and direction confusion have practical applications in fields such as telecommunications, where understanding the direction of energy flow is crucial for efficient transmission of signals. They also play a role in the design of technologies that utilize electromagnetic radiation, such as solar panels and antennas.</p>

1. What is the Poynting vector and how is it related to direction confusion?

The Poynting vector is a mathematical concept that represents the direction and magnitude of electromagnetic energy flow. Direction confusion refers to the difficulty in determining the direction of energy flow in certain situations, such as when there are multiple sources of electromagnetic radiation.

2. How does direction confusion affect scientific research?

Direction confusion can lead to incorrect interpretations of experimental results and can hinder the progress of scientific research. It is important for scientists to carefully consider the direction of energy flow when conducting experiments and analyzing data.

3. What factors contribute to direction confusion in the Poynting vector?

Direction confusion can be caused by factors such as the presence of multiple sources of electromagnetic radiation, reflections and refractions of radiation, and the orientation of the observer relative to the sources.

4. How can direction confusion be minimized in scientific experiments?

To minimize direction confusion, scientists can carefully design their experiments to control for the factors that contribute to it. This may include using shielding to block out unwanted radiation sources or carefully positioning the observer relative to the sources.

5. Are there any real-world applications of the Poynting vector and direction confusion?

Yes, the Poynting vector and direction confusion have practical applications in fields such as telecommunications, where understanding the direction of energy flow is crucial for efficient transmission of signals. They also play a role in the design of technologies that utilize electromagnetic radiation, such as solar panels and antennas.

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