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On 04/11/05 17:49, Mangala Joshua wrote:ring
I have a question about a demonstration showing Lenz's Law. Whilea ring is hanging if we bring a fairly strong magnet towards it the
ring repels and when the magnet is moved out the ring attracts. We
usually don't see this effect if we have a ring that has a slit in it.
However today I used a very strong magnet and I was able to move the
with the slit._______________________________________________
I hypothesize that the material of the split ring
has nontrivial cross-sectional area. So ... consider
the following path, where there is a high current
density just inside the surface of the material.
_________________
| |
|\/ ______ /\|
| | | |
| | | |
| | |____|
| /\| ____
| | | |
| | | |
| |______| |
|\/ /\|
|________________|
This is the celebrated "skin effect" discussed in
E&M books (e.g. Jackson).
The total force depends on the area from which the
field is exluded by the screeing currents. For
the split loop, the area will just be the projected
area of the material. For the unsplit loop, the
area will be larger, namely the whole area
encompassed by the loop, including the hole.