Re: [Phys-l] induced electric field

[Brian Whatcott <betwys1@sbcglobal.net>]

Sympathizing completely with the lack of direct response to your 
question as initially posed, the idea of using the center portion of the 
field plot that Bob depicted, as  answering your infinite field question 
leads me to maintain my earlier guess and prejudice -  that a search 
loop in the far interior of a quasi-infinite region of increasing 
magnetic field will detect a circulating current that does not vary with 
loop position while not sensing a linear e field
there, for the reason you gave.

Brian W

LaMontagne, Bob wrote:
> I am not sure what reconciled means here. I am impressed with Bob's solution to the rectangular loop problem - it's one I will file away for future reference. But my comments were directed to a statement of the problem that did not specify a rectangular loop - just a uniform dB/dt presumably over all space - a far less daunting problem than those that have been solved for us so elegantly - but one I nevertheless still claim cannot have a solution without some prefered direction or boundary in space being given.
>
> Bob at PC
>
> ________________________________________
> From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Brian Whatcott [betwys1@sbcglobal.net]
> Sent: Thursday, November 26, 2009 4:36 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] induced electric field
>
> I wonder if Bob and Phillip are now reconciled to the beautifully drawn plots from Bob for the field conditions specified by David?
>
> Brian W
>
> LaMontagne, Bob wrote:
>   
> > /snip/
> > I have not assumed that the E field is tangential to the loop. I am only assuming that because no boundaries are stated that no matter where I put the loop the integral (EMF) must be the same because nothing distinguishes one postion of the loop from another./snip/
> >
> > If a boundary is specified then the symmetry is broken and I agree with you and JD that the field at any point can be easily argued to be unique and can probably be found by some clever argument.
> >
> > Bob at PC
> >
> >     
>
>   
> > ________________________________________
> > From: Philip Keller [PKeller@holmdelschools.org
> >
> > /snip/ suppose you cannot assume that the field has the same magnitude at all points on the loop -- say because it is that second loop you and I were both thinking of, near but not touching the first.  At the point where the second loop is nearest the first, the electric field is pointing "the wrong way" - not in the direction of the current. /snip/the problem shows up regularly on the EM section of the AP physics C test but I don't recall symmetry or boundary conditions ever being mentioned.
> >