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Eddy Currents and Non Ferrous Metals.

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Eddy currents can be induced in non-ferrous metals as demonstrated here.....(These currents produce magnetic fields which interact with each other)........

https://www.youtube.com/watch?v=Yu1uRvErM80


Z.
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    And, copper or aluminium can react as if they  are ferrous or magnetically affected.

    Imagine It - Eddy current science - YouTube


    Z.
  • 0
    Strictly speaking Z those are not Eddy currents. Take a maglev train. There are a lot of coils that induce a current into a very solid piece of Aluminium. The current in the Ali produces a magnetic field, which then interacts with the one inducing the current, and applies a force to the aluminum.  When I was at school there was a "demountable transformer" with a mains winding. The core could be left open, giving an upright core section about 18" long. One could float rings of Ali foil and stuff on the field around the core. I made a copper ring, fitting over the core but 10mm thick and 25mm wide, with a silver-soldered joint. Resistance a few micro-ohms. The mains coil was about 1 turn per volt so I had tens of thousands of amps flowing in the ring. It got very hot quite quickly! The force on this was very substantial (my idea) and made a very effective ring gun which made big marks in the ceiling when the power was applied. In fact, it took several kilowatts, and the ring would almost support a suitable boy, say 50kg, and push him at the ceiling! The teacher was not awfully impressed but was seen using the ring to show another class how powerful magnetic fields could be. The Americans used something similar as a catapult on a nuclear-driven Aircraft Carrier, it accelerated planes to a couple of hundred miles an hour in about 50 metres, the pilots complained as it was many more "G" than the old steam type which was considerably longer and required the plane engine at full afterburn too. The electric one saved significant fuel in the fighter, a great advantage.


    You can see Eric Laithwaite demonstrating both of these things on youtube, but they are not Eddy current driven, just normal induction.
  • 0
    Ah yes, Eric's  lecturing style was something else - he really did understand it.

    You do need the free time to let it soak in to fully appreciate all of it.


     

  • 0
    mapj1:

    Ah yes, Eric's  lecturing style was something else - he really did understand it.

    You do need the free time to let it soak in to fully appreciate all of it.


     



    Professor Laithwaite is a wonderful  lecturer and demonstrator. The video clip is fascinating. Thanks.


    Z.


  • 0
    My text book dated 1898 entitled "Electrical Engineering" by Sligo and Brooker also  calls Eddy currents Foucault currents. We can call them that if preferred.

     

    Currents of Foucault


    Currents of Foucault

    Foucault currents are the currents induced in masses of conducting metal that are immersed in a variable magnetic field or that, in motion, through a constant or variable magnetic field. In any case, it is the variation of the magnetic flux that generates these currents. The phenomenon was discovered by the French physicist Jean Bernard Léon Foucault in 1851.





    Z.
  • 0
    We can call eddy currents that if you like,  but please note,  it  is not currents that the lines on your diagram represent.

    The lines in the diagram are magnetic fields, quite a different thing, and at right angles to the current.

    Both the driving currents, and any induced Foucault  currents associate with those lines of magnetic field are entirely out of the plane of the screen.


    Mike


    * (magnetic field lines tell you the pointing direction of an imaginary small compass, lines of current are about moving electric charges . This was not fully fixed in 1898 you may do marginally better with Electricity and Magnetism by Bleaney and Bleaney 1957 vol 1. however it is not a light read.).
  • 0
    Another good primer for the interactions of electricity and magnetism and much easier to digest.

     

  • 0
    mapj1:

    We can call eddy currents that if you like,  but please note,  it  is not currents that the lines on your diagram represent.

    The lines in the diagram are magnetic fields, quite a different thing, and at right angles to the current.

    Both the driving currents, and any induced Foucault  currents associate with those lines of magnetic field are entirely out of the plane of the screen.


    Mike


    * (magnetic field lines tell you the pointing direction of an imaginary small compass, lines of current are about moving electric charges . This was not fully fixed in 1898 you may do marginally better with Electricity and Magnetism by Bleaney and Bleaney 1957 vol 1. however it is not a light read.).


    Yes Mike I know that the lines are magnetic "flux" or "field." it is these that create the unwanted eddy currents that can cause problems and energy wastage. My McKenzie Smith & Hosie book of the 70s entitled Basic Electrical Engineering Science says: "If a loop of conducting material is linked by a varying flux, an E.M.F.  is induced in the loop and a circulating current will flow round the loop. The current in the loop is termed an eddy current. The eddy current flows around a path of one turn which is effectively a short circuit.  "I am not disputing the arrangement of the parts of this process. The film about electromagnetic waves was very interesting. Thanks Mike.


    Z.


     


  • 0
    I first saw Eric in Gyroscope mode in Engineer thru the looking glass at RI Lectures. Great show, then he did the Maglev, Wow.


    He did not say Newton was wrong

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