Re: EM Induction - A conceptual question

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

Here is a possible experimental way to answer Chuck's
question (see below).  He wants to know if a change in
the flux density, while the flux remains constant, will
induce the emf in the larger loop. My guess is NO but
I will be ready to change my mind if the experimental
answer is YES.

A large circular loop (N>1 if necessary) has a
galvanometer in it, an indicator of the presence of
the induced emf. Suppose two concentric solenoids
are used to create a magnetic flux inside the large
loop. Is it possible to design a setup in which the
flux from one solenoid increases while the flux from
another decreases quickly in such a way that the total
flux remains constant? If so then the setup can be used
to test for the presence or absence of the induced
emf. Several approached come to mind but I have
no time to investigate. A good project, I suppose.
Ludwik Kowalski

chuck britton wrote:

> 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.