Re: induced emf and eddy currents

[igal@vms.huji.ac.il (Igal Galili)]

>        All "motional" emfs can be accounted for from Faraday's law.
> There is no need to introduce them separately (although that often is
> done).
>
> Mark


Mark, colleagues,

        Feynman had a different view (please, look).  Faraday's law,  or
"the flux rule" (in Feynman's words) is an empirical law, limited in its
applicability.  It cannot be fundamental as it is integrative.  Fundamental
laws are differential ( I quote Feynman.)  I think, integrative laws serve
us  introducers to the microscopic world and not more than this.  The
opposite to yours statement is a limited truth:

Faraday's law can be derived from "motional" emf (more precisely, magnetic
force) plus the complementary  phenomenon of the curly emf.  (see also
Berkeley course E&M by Purcell).

To see in Faraday's empirical  law the physical fundamental is an illusion.
The current situation with induction emf in introductory physics courses
is odd.   But the reason is that we cannot do any better within
pseudo-classical theory of E&M.  This was exactly the point where physics
had a problem by the end of the twentieth century, and it was solved by
Einstein within the relativity theory.  I wrote my opinion on the subject,
the preferable way to teach E&M nowadays,  it will seemingly come out in
the next AJP.    There you can find more examples of the limited validity
of Faraday's law.
             Another thought.  If we do not teach our students  historical
and philosophical aspects of this subject, I think we just reduce the
number of students who can understand it to the minimum.
Best regards to you all.

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Igal Galili
The Science Teaching Department        Ph:             INT+972-2-6584097
The Hebrew University of Jerusalem   FAX:          INT+972-2-6585708
Jerusalem 91904  ISRAEL                         E-mail:   igal@vms.huji.ac.il
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