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Unconventional Dynamo (TPT, April, 2002)



The April issue of The Physics Teacher has an article that grabbed my
attention (once I got around to opening the copy)

I think that the Note on page 220 by Wojciech Dindorf deserves our attention.
It was in the summer of 1999 that my colleague, Hugh Haskell, and I
had the opportunity of having Herr Dindorf demonstrate this exact
devise. I must admit that the exposition was less than adequate to
satisfy my cynical eye. We were gathered in a Viennese schoolroom,
having just watched a set of demonstrations being performed for the
students who were attending the International Young Physicists
Tournament. Herr Dindorf pulled his model out of his briefcase and
offered to let us analyze it's operation. The mechanical stability of
the rotating device and the 'sensitivity' of the galvanometer were
less than convincing.

I need either a better constructed and operated device OR a
reasonably clear Maxwellian explanation of the 'effect' to become
convinced.

For those who have access to the April issue - go to it! Let's hear
YOUR analysis.

For the REST of you - well - I'll TRY to explain the mechanicals of it.

Create a 'tubular magnet' with north poles outward.

Mount it on an insulating axle. (wooden in this example)

Attach a crank to one end of the axle so that the magnet can be
rotated around it's axis of symmetry.

At the opposite end of the axle, attach a second crank that is
attached to a 'half loop' of stiff wire. This 'half loop' connects
electrically to brass 'slip rings' at each end of the axle.

The two cranks are mechanically separate, so one can rotate EITHER
the magnet OR the 'half loop' independently.

Finally, a 'sensitive' galvanometer is attached across the two 'slip rings'.

Three situations are enumerated:

1) The loop moves around the stationary magnet.

2) The magnet rotates while the loop is stationary. and

3) Both the magnet AND the loop rotate together
with no change in position relative to the other.

In which cases (if any!) will the galvanometer indicate that emf
and/or current is being generated.

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Chuck Britton Education is what is left when
britton@ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 416-2762 (not in summer) Albert Einstein, 1936