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Current carrying conductor has a net force parallel to earth, why?

  1. Jul 19, 2014 #1
    I am not sure if I should start a new thread or revive an old thread this because it is the same topic.

    Location of tests: Scandinavia

    I simply want to know why and how a current carrying conductor parallel to earth surface moves perpendicularly to the current flow and parallel to earth surface. I discovered this by accident while in the lab hanging wire from a battery. I made many experiments, it is not local effects in the house. the conductor simply always moves perpendicular to the direction of current regardless of where I point the conductor. I am a little puzzled as to how and what the cause is in making the wire move.

    I thought that it is the magnetic field of earth inducing a Lorentz force on the wire. this would make perfect sense since IF the assumed magnetic direction of earth points perpendicular to earth surface there would be a Lorentz force on the wire But, the magnetic direction of earth -if I know correctly -runs parallel to the surface so any wire should instead want to move either up or sideways depending on the direction of the current relative to earth S.N.E.W.?

    Sofar however, the conductor always moves perpendicular to the conductor and parallel to earth surface regardless if I point the conductor South north or east west or any other combination.
    The conductor was also a straight lightweight rigid piece of aluminium foil hanging from a battery by two other strait light alu foils.. I put the conductor away from everything, on the table and also away from the table or anything else I tried this outside too.. I took a piece of ferromagnetic material very close besides the current carrying conductor, and still the conductor moved perpendicular to its current unaffected by the intentionally placed ferromagnetic material... could it be that the magnetic direction is indeed perpendicular to earth surface in the northern part of Earth?I am actually confused here and thought that the experts here may help me out?


    Maybe a better angle to solve this is the question of how the direction of the magnetic field looks like on the north part of earth but not directly on the pole of the earth.

    Picture shows the motion direction as well.
     

    Attached Files:

  2. jcsd
  3. Jul 19, 2014 #2
    There is a vertical component to the magnetic field, wich gets bigger the nearer you get to the magnetic poles.
    See the wikipedia article: http://en.wikipedia.org/wiki/Magnetic_dip and its map of magnetic inclination.
    In Scandinavia the magnetic field lines make an angle of about 70 degrees with the horizontal.

    The Lorentz force due to the vertical component of the magnetic field will be perpendicular to both the current, and the magnetic field, so it will be parallel to the ground and perpendicular to the wire.

    The lorentz force due to the horizontal component will be straight up or down, and the only result will be that the horizontal wire will appear to be slightly heavier or lighter, wich I don't think you'd notice.
     
  4. Jul 20, 2014 #3

    sophiecentaur

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    Applying BIL (our well known electromagnetic friend) you get a very tiny force unless you're using vast values of current.
     
  5. Jul 20, 2014 #4
    so it seems that it is the vertical component that is intercepted and cause of motion in the tests if I understand this?
     
  6. Jul 20, 2014 #5

    sophiecentaur

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    You would need to know the actual value of current involved, to know (estimate) if the force could possible be responsible for any force that was measured.
     
  7. Jul 20, 2014 #6

    mfb

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    Well, we can play around with values: the strength of the magnetic field is around 50µT (approximately everything vertical in Scandinavia), on a wire with a length of 1m and a current of 1A this applies a force of 500µN. Enough to accelerate 1g of wire with 5cm/s^2, with a very low friction this could be notable. This mass allows to make copper with a cross-section of .1mm^2 and a resistance of .17 Ohm/m. Certainly a possible setup that will allow even higher currents.
     
  8. Jul 23, 2014 #7

    mfb

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    I tested this (in Germany): I used extracted fibres from a cable, connected three of them to a thin ~.5m wire suspended at both ends and sent 2 A through. Even with the still notable stiffness of the wire its equilibrium position shifted notably with current flowing.
    A strong magnet nearby increased the effect significantly.

    Yes, it is easy to see the influence of the magnetic field of earth on a wire.
     
  9. Jul 23, 2014 #8
    mfb, nice! I used many amperages. I used mostly 2 A though too and even ordinary 3mm silicon insulated cables moved very noticeably. So yeah 2A is more than enough to show the motion. You are at lower location than me. So the force you have should be less?.



    1- is your wire-motion direction the same as the one in my picture from first post?
    2-It would be interesting to ask someone do this little experiment at the equator , the force should be a lot smaller and almost negligible if I understand this?
     
  10. Jul 25, 2014 #9

    mfb

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    That difference should be small compared to other experimental differences.

    Interesting point - it is not. But the motion I see agrees with the magnetic field of earth.

    Right (the green line)
     
  11. Jul 25, 2014 #10
    Interesting that your observed motion is not the same that I have(the one in the drawing is the direction I have observed)
     
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