Magnetic field and electric field induce one another forever

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Discussion Overview

The discussion revolves around the relationship between changing electric and magnetic fields, particularly in the context of circuits involving capacitors and batteries. Participants explore whether this interaction can continue indefinitely and the implications of various laws, such as Ampere-Maxwell and Lenz's Law, on the behavior of these fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that a changing electric field produces a magnetic field and vice versa, suggesting a continuous cycle that could theoretically persist indefinitely.
  • Others argue that while electric and magnetic fields are intertwined, the mathematical treatment differs from simple circuit analogies, particularly in the case of photons where the fields are in phase.
  • It is noted that in circuits with batteries and capacitors, the fields do not oscillate but rather reinforce each other, challenging the notion of perpetual induction.
  • Some participants emphasize that for oscillation to occur in a circuit, inductance is necessary, and without it, a DC voltage applied to an ideal capacitor will not lead to oscillation.
  • There is a discussion about the relevance of magnetic fields in ideal components, with some asserting that they have no effect on ideal voltage sources or capacitors.
  • One participant raises the consideration of Lenz's Law, questioning whether induced currents and their corresponding magnetic fields would oppose the original fields, potentially preventing an infinite net field.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the interaction between electric and magnetic fields, with some asserting a continuous cycle and others emphasizing the limitations imposed by circuit components and laws like Lenz's Law. The discussion remains unresolved regarding the implications of these interactions.

Contextual Notes

Limitations include assumptions about ideal components versus non-ideal wiring, the dependence on specific circuit configurations, and the unresolved nature of how these fields interact over time.

Joker93
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A changing electric field produces magnetic field and vice versa.Does that mean that this process will carry on forever?Think of a circuit with a capacitor.The magnetic field due to the current at a point on the wire(with Ampere-Maxwell law).But current was changing with time,so it also meant that the magnetic field changed.And a changing magnetic field produces an electric field,so we have to go back again from the start with the Ampere law.It seems that this will go on forever.What is the final magnetic and electric field that i have to calculate?
 
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Well it is called the electromagnetic field after all.

Most mind bending is when you consider changes in inertial reference frame. Viewed from another frame, electric becomes magnetic and magnetic becomes electric.

Yes they are intertwined, but the math is not identical to your circuit analogy. In a photon, the electric and magnetic fields are in phase, not 90 degrees out of phase as intuition and circuit analysis would suggest.
 
anorlunda said:
Well it is called the electromagnetic field after all.

Most mind bending is when you consider changes in inertial reference frame. Viewed from another frame, electric becomes magnetic and magnetic becomes electric.

Yes they are intertwined, but the math is not identical to your circuit analogy. In a photon, the electric and magnetic fields are in phase, not 90 degrees out of phase as intuition and circuit analysis would suggest.
In the example where i have a circuit with battery and capacitor,they do not seem to be oscilating with each other.they just reinforce one another
 
Adam Landos said:
In the example where i have a circuit with battery and capacitor,they do not seem to be oscilating with each other.they just reinforce one another

Circular reasoning is not the same thing as oscillations. For your circuit to oscillate, there.must also be som inductance. If you apply a DC voltage to an ideal capacitor, with no inductance it will not oscillate and the magnetic field is irrelevant.
 
anorlunda said:
Circular reasoning is not the same thing as oscillations. For your circuit to oscillate, there.must also be som inductance. If you apply a DC voltage to an ideal capacitor, with no inductance it will not oscillate and the magnetic field is irrelevant.
With DC current,before steady-state you will have a time changing current.So the induced magnetic field is not irrelevant.
 
But a magentic field has no effect on an ideal voltage source or an ideal capacitor. In that sense it is irrelevant.

But non-ideal wiring always has some nonzero inductance and capacitance. Is that what you are thinking of?
 
anorlunda said:
But a magentic field has no effect on an ideal voltage source or an ideal capacitor. In that sense it is irrelevant.

But non-ideal wiring always has some nonzero inductance and capacitance. Is that what you are thinking of?
No,no.Forget the capacitor or battery.They are just there to give us the time changing current.Suppose you want to calculate the magnetic field using the Ampere-Maxwell law on a point of the wire.Then you find a time changing magnetic field.But that means(from the same law)that you will also have induced electric field that changes with time.And that causes yet another induction of magnetic field and this goes on and on.
 
Don't you also have to consider Lenz' Law here? So wouldn't the induced current and it's corresponding magnetic field produced oppose the original one, so a net field is not infinite?
 

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