- #1
qh4305
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Why is the energy of a circuit placed in a magnetic field at infinity zero?
Why is the energy of a circuit in a magnetic field at infinity zero?
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Discussion Overview
The discussion revolves around the question of why the energy of a circuit placed in a magnetic field at infinity is considered to be zero. Participants explore concepts related to energy in circuits, magnetic fields, and potential energy, with a focus on theoretical implications and formula derivation.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- One participant humorously suggests that the energy might be zero because batteries would be drained on the way to infinity, questioning the initial premise.
- Another participant expresses confusion about the scenario, asking for clarification on what is meant by "at infinity" and the nature of the magnetic field involved.
- A participant mentions an assumption made regarding the energy of the circuit at infinity being zero, but acknowledges uncertainty about its validity in scientific contexts.
- Several participants request the formula and context of the question to provide more targeted assistance.
- One participant notes that static magnetic fields do not induce voltage and thus do not contribute energy to a circuit, while time-varying magnetic fields do, depending on their intensity.
- Another participant discusses how the amplitude of time-varying fields decreases with distance, suggesting that only the magnetic field values at the circuit matter for energy considerations.
- A later reply introduces the idea that classical physics may not fully explain the energy behavior of photons in relation to distance.
Areas of Agreement / Disagreement
Participants express varying levels of confusion regarding the initial question and the assumptions made. There is no consensus on the nature of the energy at infinity or the validity of the assumptions presented, indicating multiple competing views and unresolved aspects of the discussion.
Contextual Notes
Participants highlight the need for clarity regarding the definitions and conditions of the scenario, including the type of magnetic field and the specifics of the circuit in question. There are unresolved mathematical steps and assumptions that affect the discussion.
- #2
berkeman
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Because the batteries get drained on the way there? It's a long trip, after all. 
But seriously, what are you talking about? Are you confusing gravitational potential energy (GPE) with electrical energy?
But seriously, what are you talking about? Are you confusing gravitational potential energy (GPE) with electrical energy?
- #3
qh4305
- 4
- 1
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?berkeman said:Because the batteries get drained on the way there? It's a long trip, after all.
But seriously, what are you talking about? Are you confusing gravitational potential energy (GPE) with electrical energy?
p/s:
sorry for my english
- #4
sophiecentaur
Science Advisor
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Show us the formula and the context of your question. That may help you to get an answer.qh4305 said:
- #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.
Maybe a simple sketch would help.
- #6
qh4305
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sophiecentaur said:
- #7
qh4305
- 4
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sophiecentaur said:
Is this a correct proof?
- #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.
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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