Re: EM Induction - A conceptual question

[chuck britton <britton@NCSSM.EDU>]

On Friday, April 12, 2002, at 12:02 PM, Fakhruddin, Hasanbhai wrote:

> Hello everyone!
>
> This question has nagged me for some time.  I will appreciate your
> indulgence in this.
>
> Imagine a circular loop of wire of radis R.  A uniform magnetic field=
>  is
> distributed perpendicular to its surface and confined to a concentric
> circle of radius r < R. =20
       Note that the B-field is said to be confined to a concentric circle
with radius LESS than that of the loop.

       Note also that the B field is said to  be uniform.

       Let's ignore the fact that these two are mutually exclusive and
PRETEND that the B field is confined within the loop. uniform or not.

MY question is: IF the confined B field expands and contracts while still
being always INSIDE the loop, will an emf be induced.

I am requiring that the integral of BdA be CONSTANT but the total A is
oscillating in size, but is always less than the area contained by the
loop.

       Those of us who are hopelessly addicted to Webers (lines of magnetic
flux) would ssay that we are requiring the total webers contained within
the loop is not changing, just the DENSITY of the webers (B) is changing
in magnitude.

               And I will SWEAR that I have seen several references to the
quantum limit of magnetic field density, expressed in terms of the usual
gang of fundamental constants. Doesn't this mean that the 'nonexistant'
weber lines are discrete lines???

       (Leigh Palmer was adamantly opposed to this idea - but I need more
convincing than that.)

>  Will the change in the magnetic field strength induce a current (emf=
> )
> in the loop?
>
> By the Faraday's law there should be an emf induced becuse of changin=
> g
> flux.  However, my contention is that B-field lines are not "physical=
> ly"
> linked to the loop.  Why should changing field affect anything in the
> loop? =20
>
> -Hasan Fakhruddin
       I am asking these previous questions also, with the restrictions and
variations stated above.