Re: induced emf and eddy currents

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Wed, 18 Jun 1997, Nick Steph wrote:

>           Consider a conducting rod of length L, moving
> perpendicularly through a UNIFORM magnetic field, B, at a constant velocity,
> v.  An observer in the lab will detect a potential difference across the rod, 
> PD = BLv.  What about an observer on the rod?  According to special relativity,
> she must detect it also; but what does she consider to be the cause?

Having thoroughly discredited my authority in this thread, I see no reason
to let humility begin standing in my way now. 

The observer on the rod sees charge separation caused by the background
electric field, the charge separation is just that necessary to eliminate
the field within the rod.  Since there are no time varying magnetic
fields, she can use a voltmeter with impunity and the voltmeter will
confirm that there is no PD between the ends of the rod. 

I'm not sure what it is about special relativity that should make us
expect her to see the same result as a "stationary" observer.  After all,
if a "stationary" observer attaches the leads of a "stationary" voltmeter
to the ends of the rod, the leads will probably form a loop with a time
varying area and, thus, magnetic flux.

John
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