Why is the energy of a circuit placed in a magnetic field at infinity equal to zero?

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qh4305
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Why is the energy of a circuit placed in a magnetic field at infinity zero?

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  • #2
berkeman
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Because the batteries get drained on the way there? It's a long trip, after all. :wink:

But seriously, what are you talking about? Are you confusing gravitational potential energy (GPE) with electrical energy?
 
  • #3
qh4305
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Because the batteries get drained on the way there? It's a long trip, after all. :wink:

But seriously, what are you talking about? Are you confusing gravitational potential energy (GPE) with electrical energy?
I had a bit of a problem with proving a formula, and I made myself an assumption that the energy of the circuit placed in a magnetic field at infinity would be zero, but maybe that doesn't hold true for science, engineering, and so on. The formula that I am proving is the formula for calculating the magnetic energy of a closed circuit in a magnetic field, I used the convention that the work of the magnetic force is equal to the decrease in potential energy, but now I think it is not quite right. Can you help me prove this energy formula?
p/s:
sorry for my english

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  • #4
sophiecentaur
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I had a bit of a problem with proving a formula,
Show us the formula and the context of your question. That may help you to get an answer.
 
  • #5
DaveE
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I think we are all confused about the scenario you are asking about. What's at infinity, compared to what? What sort of magnetic field? What made it? What do you mean by a circuit? Is it just a loop of wire?

Maybe a simple sketch would help.
 
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  • #6
qh4305
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Show us the formula and the context of your question. That may help you to get an answer.
1621898377089.png
thanks.
 
  • #7
qh4305
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Show us the formula and the context of your question. That may help you to get an answer.
1621898765040.png

Is this a correct proof?

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  • #8
DaveE
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Sorry, I still don't know what you're asking about. Maybe someone else will figure something out.

Here are a couple of general comments about energy created in a loop of wire from magnetic fields:
- DC (static) magnetic fields don't induce any voltage and thus no energy in a "circuit".
- The energy from a time varying magnetic field will be proportional to it's intensity.
- Time varying fields propagate to fill more space and as a result their amplitude decreases. As the distance from the source goes to infinity, the amplitude approaches zero.
- The only thing that matters to the circuit in question is the magnetic field values at the circuit. The only value in examining the field at distant points is if that helps characterize it at the circuit.
- This is classical physics. Most of this doesn't make sense if you consider that a photon could travel the length of the universe, or a short distance, and carry with it the same energy in either case.
 

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