THE LIBRARY OF SOPHIA OF WISDOM III THE SOPHIA OF ALL SOPHIA OF WISDOMS
AKA
CAROLINE E. KENNEDY________________________
MARCH 18, 2007
The electromagnetic field as a feedback loop
The behavior of the electromagnetic field can be resolved into four different parts of a loop: (1) the electric and
magnetic fields are generated by electric charges, (2) the electric and magnetic fields interact only with each other, (3)
the electric and magnetic fields produce forces on electric charges, (4) the electric charges move in space.
The feedback
loop can be summarized in a list, including phenomena belonging to each part of the loop:
charges generate fields
Gauss's law Coulomb's law: charges generate electric fields Ampère's law: currents generate magnetic fields () the
fields interact with each other displacement current: changing electric field acts like a current, generating 'vortex'
(curl) 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 Maxwell-Hertz equations: simplified version of Maxwell's
equations electromagnetic wave equation fields act upon charges 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 () charges move continuity equation: current is movement of charges Phenomena in the list are marked
with a star () if they consist of magnetic fields and moving charges which can be reduced by suitable Lorentz transformations
to electric fields and static charges. This means that the magnetic field ends up being (conceptually) reduced to an appendage
of the electric field, i.e. something which interacts with reality only indirectly through the electric field.
