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Friday, 1 July 2011

The electromagnetic field as a feedback loop

The electromagnetic field as a feedback loop

The behavior of the electromagnetic field can be resolved into four different parts of a loop:
  • the electric and magnetic fields are generated by electric charges,
  • the electric and magnetic fields interact only with each other,
  • the electric and magnetic fields produce forces on electric charges,
  • the electric charges move in space.
A common misunderstanding is that the quanta in the field are the same as the charged particles that generate the fields. In our everyday world, charged particles, such as electrons, move slowly through matter typically on the order of a few inches (or centimeters) per second[citation needed], but fields propagate at the speed of light - approximately 186 thousand miles (or 300 thousand kilometers) a second. The mundane speed difference between charged particles and field quanta is on the order of one to a million, more or less. Maxwell's equations relate the presence and movement of charged particles with the generation of fields, that can then affect the force on, and move, other slowly moving charged particles. Charged particles can move at relativistic speeds nearing field propagation speeds, but, as Einstein showed[citation needed], this requires enormous field energies, which are not present in our everyday experiences with electricity, magnetism, matter, and time.
The feedback loop can be summarized in a list, including phenomena belonging to each part of the loop:
  • charged particles generate electric and magnetic fields
  • the fields interact with each other
    • changing electric field acts like a current, generating 'vortex' of magnetic field
    • Faraday induction: changing magnetic field induces (negative) vortex of electric field
    • Lenz's law: negative feedback loop between electric and magnetic fields
  • fields act upon particles
    • Lorentz force: force due to electromagnetic field
      • electric force: same direction as electric field
      • magnetic force: perpendicular both to magnetic field and to velocity of charge
  • particles move
    • current is movement of particles
  • particles generate more electric and magnetic fields; cycle repeats

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