faradays overlooked discovery...

Discussion in 'Off Topic' started by HeadSmess, Jun 25, 2015.

  1. HeadSmess

    HeadSmess Well-Known Member

    well, not entirely overlooked(n machine is a good topic to follow, or homopolar generators), but sort of unknown. 20th december, 1831 or so, he conducted yet another experiment with this peculiar phenomenom between magnets and wires that at the time was a complete mystery...(inductance....the production of electricity... etc...)

    get a bar magnet.

    place it with an axle running N-S.

    attach a wire to to axle, and a wire to the centre of the magnet.

    spin the magnet.

    a dc current is produced between the wires as indicated on a galvanometer.

    ok. thats weird.

    so, now get two rather flat disc magnets.

    attach them to an axle so once again, its parallel with the N-S axis.

    get a flat copper disc and place it between the two magnets.

    hold it still whilst spinning the magnets.

    attach wires as previous, one to axle and one to rim of copper disc.

    nothing happens!



    moving magnetic field, condu... hang on.

    maybe the magnetic field doesnt move WITH the magnet?

    hold the magnets still, spin the disc...

    a current is produced! and the disc was sort of hard to turn!

    the basis of eddy current motors that drive your electricity watt meter ;)

    but quite a bizarre effect. we now call it inductance or lenz's law or some such thing... a conductor moving through a magnetic field... easy peasy now...

    so...thats strange, but what happens if we rotate the disc AND the magnets together?

    well, we get a current. and the rather peculiar thing is that it doesnt seem to produce the same back-emf.

    which in a normal generator set, we see as the generator "loading down" due to inductance and other effects.

    i try a lil quick experiment last night...

    get some iron filings and a magnet, do the lines of force test.

    you see the lines of force as little spikes...

    you slide the magnet slightly, and you notice the spikes tend to flop over as the field bends... but the base of them, the point they emanate from...does not move with the magnet; to a degree as the iron filings tend to cling to the magnet. but! rotate the magnet, and the spikes stay dead still....
    this is what farady refered to as "the peculiar singular nature of the magnetic field that appears to remain separate from the iron (magnetic material)"

    the magnetic field does NOT move with the magnet itself....

    YET! when you rotate the lot as a whole, paper, filings and all, they DO move with the magnet...

    once again...its very very peculiar....

    and yes, homopolar generator do work, have been used to a degree as gen sets for electroplating in the late 1800's, but the fact that they dont produce the same back emf has never really been investigated...

    besides producing DC current, at huge currents...low potentials... talking thousands of amps at less than a volt even...

    ill leave it there as food for thought

  2. jaguar

    jaguar Well-Known Member

  3. HeadSmess

    HeadSmess Well-Known Member

    they do... in electricty meters as eddy current motors...when the magnetic field induced by an electromagnet is held static with a conductive disc free to rotate. feed the electromagnet AC and the induced eddy currents produce torque to rotate the disc... at an rpm governed by current therefore indicating the power flowing through it.

    as motors...they require huge currents due to the "single turn winding" to produce enough magnetic flux to produce any torque.

    hence why they only make generators.

    the homopolar is slightly different in that the magnets themselves remain stationary. they can be rotated as well, as a single unit, with the conductor. thats whats so strange...