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

On 15 Jul, 07:55, phil-news-nos...@xxxxxxxx wrote:
On Mon, 14 Jul 2008 11:16:39 -0700 (PDT) blackhead <larryhar...@xxxxxxxxxxxx> wrote:
| On 12 Jul, 12:19, phil-news-nos...@xxxxxxxx wrote:
|> It seems there is an error in this Wikipedia article:
|>
|> ? ?http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction
|>
|> Faraday's law says the induced EMF is in proportion to the rate of CHANGE
|> (my emphasis) of the magnetic flux. ?The article describes this much OK.
|> Later on, the article then says:
|>
|> ? ? In the case of motional EMF, the idea is to move all or part of the
|> ? ? circuit through the magnetic field, for example, as in a homopolar
|> ? ? generator.
|>
|> But this last case is a situation where the magnetic flux does not change.
|> Isn't this the aspect that Faraday saw as a paradox because it did not obey
|> his law of induction? ?Apparently he realized that no flux change happened
|> when he rotated the magnets with the rotating disk in his unipolar generator.
|>
|> 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.
|
| Which is correct, as far as Faraday's Law is concerned. The induced
| EMF around a closed circuit is equal to the rate of change of flux
| through the circuit and independent of whether it's the conductor or
| the magnetic filed which is "moving".

But the Lorentz law is not about change of flux.

The Lorentz force is the solution to the differential form of
Faraday's Law, Curl E = -dB/dt.

Look at the abstract of this paper for example:

-------
<http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?
tp=&arnumber=995632&isnumber=21481>

Deriving the Lorentz force equation from Maxwell's equations

Abstract

A derivation of the Lorentz force equation is presented here based on
one of Maxwell'sequations, Faraday's law. The presentation is intended
to be understandable by those who have not recently studied
electromagnetism
-------

Blackhead


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