Re: Error in Wikipedia article: Faraday's law of induction

On Jul 12, 7:19 am, phil-news-nos...@xxxxxxxx wrote:

As I understand all this, there are TWO ways to induce electricity from a
magnetic field:

1. A conductor at a right angle to the magnetic field alignment experiencing
a change in the magnetic field flux density (strength). [Faraday's law
of induction]

2. Motion of a conductor at right angle to the magnetic field alignment and
simultaneously at right angle to the line of the conductor. [Fleming's
right hand rule, Lorentz force law]

The article seems to be trying to convert everything into one.

Not really. Yes there are two ways and electric field can be produced
in a conductor (wire). One would be the relative motion between a
magnetic field and the conductor. That is related to the Lorentz force
law on charges. A simple example would be the moving of a magnet in
and out of a coil of wire. Also generators work on this principle and
the calculation of operation this way is usually called "flux cutting"
methods. The wires pass through the flux "cutting" it and producing
Lorentz EMF inside the wires.

The other way of producing electric fields inside wires is known as
"flux changing". IF we have two coils of wire and we put a current
through one of them, a pulse of voltage appears in the other. Note
that NOTHING is moving so there is no "flux cutting". Only the flux
through the second coil is changing because the current in the first
coil is changing.

So now there are TWO ways to produce an "emf" in a wire by means of
magnetic flux. But flux methods of BOTH types are limited. Sometimes
they fail altogether! A Faraday generator is a perfect example. The
magnetic field is not changing so there is no flux changing. And since
the disk is solid and continuous it really isn't "cutting" the flux
either. There are other examples of geometry that show the failure of
flux methods. Feynman notes that in such cases you go back to first
principles (Maxwell's equations) no matter how handy flux methods are
in calculating answers in many practical cases. In the case of mutual
induction the Vector Magnetic Potential can be seen to play a vital
role.

There have been many attempts to convert these two things into one.
For example people have argued that as a current increases in a wire
the magnetic field expands from the wire and thus produces Lorentz
forces in neighboring wires. These theories to date have all failed.
Flux theories have all pretty much failed to be fundamental. In fact
the whole concept of "lines of flux" is rather bogus to begin with!
Not that they are not useful, mind you.

So yes, there is no combining these things. You are allowed to go
"fix" the Wikipedia article you know!

.

Relevant Pages

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