Re: [Phys-l] Question about Electromagnetic Induction

[Brian Whatcott <betwys1@sbcglobal.net>]

Fakhruddin, Hasan wrote:
> Greetings folks!
>
> Consider a circular conducting loop of radius 'a'.  Concentric and coplanar to it is a circle of radius 'b' (b<a) within which there is uniform magnetic field perpendicular to the plane of the conducting loop.  The magnetic field is varying at a rate dB/dt. 
>  
> QUESTION:  Does the induced emf in the loop depend on the radius 'a'?  If not, then can the radius 'a' take larger values without limit?  
>
> ~Hasan Fakhruddin

I idealize a model in this way.
Two rings are linked.
One ring carries an electric current, the other ring carries a magnetic 
flux.
(You will notice that does not meet your specification of a flux 
everywhere perpendicular to the plane  of the current ring, but the 
plane of the flux and that of the current can indeed be perpendicular 
and intersecting).

It is quite easy to realise the current ring, in that the ratio of 
resistivity of the ring to that of a plausible medium such as air is 
extremely low.
It is quite hard to realise a magnetic flux ring, because the comparable 
ratio of permeabilities is so  much closer to one in comparison.
A mere detail....
The current ring evidently links all the flux except the unavoidable stray.
How big can the current ring grow?  The electric field does not depend 
on the current ring's size except as is evident, the current driven by 
the varying flux is reduced by the resistance which it presents to the 
current. The field survives, though the current ring is broken, in fact.

This seems like an unprovocative conclusion, I see.

Brian W