Re: Retarded propagation of magnetic field leads to contradiction
From: Tom Roberts (tjroberts_at_lucent.com)
Date: 07/31/04
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Date: Sat, 31 Jul 2004 00:35:02 GMT
Eugene wrote:
> A magnet and a wire loop are separated by the distance R.
> If both of them are at rest, there is no current in the loop.
>
> If the magnet starts to move then (we assume that the
> magnetic field propagates with the speed of light) the current
> starts to flow in the loop only after time R/c
>
> If the magnet stands still, but the loop moves and
> crosses the magnetic lines, the current starts to flow
> immediately.
>
> As from the relativity principle both these situations should
> be equivalent, we got a contradiction.
No, they are not "equivalent". Specifically, you are measuring the
current AT THE LOCATION OF THE LOOP. So if the loop starts moving wrt
magnet there is no delay over the distance between the starting of the
motion and the measurement of the current; when the magnet starts moving
there is necessarily such a delay as the change in the magnet's field
propagates at c to the location of the loop and your measurement.
> SOLUTION OF THIS PARADOX: Magnetic field propagates
> instantaneously.
1. There is no paradox, merely a mistake on your part.
2. Changes in the magnetic field are observed to not propagate
instantaneously (it does not really make sense to discuss
"propagation" of the field itself, as field do not propagate,
only changes in them do).
Tom Roberts tjroberts@lucent.com
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