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Magnet vs CRT TV a.k.a question about magnetic poles of electrons

  1. Aug 15, 2014 #1
    When watching some videos about neodymium magnets, I came upon a very interesting phenomenon. Namely, the maker of the video put a large magnet near an old CRT TV.

    At first, a big black spot appeared on the screen. This means that the electrons were repelled from from the magnet and didn't hit the screen. After that, he turned the magnet around and approached the screen again. This time, the electrons rushed to the magnet and created one illuminated spot, leaving the other parts of the screen dark.

    My question is, why are the magnetic poles of the electrons emerging from the cathode all lined up in the same direction and why don't they 'turn around'? When I approach 1 big magnet's south pole with some small magnets' south pole, the small magnets always turn around, exposing their north pole and are attracted to the big one instead of reataining the same position and being repelled.
     
  2. jcsd
  3. Aug 15, 2014 #2

    Simon Bridge

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  4. Aug 18, 2014 #3
    Yes, I know that moving charged particles are affected by magnetic fields. But that means that 1 pole of the magnet attracts negative charge and the other one repels it. From that can we derive that one pole of the magnet has + charge and the other one has - charge or not?
     
  5. Aug 18, 2014 #4

    Nugatory

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    Charged particles are affected by magnetic fields, but not the way that you're thinking. The magnetic force a charged particle experiences depends on the particle's speed and direction. There is no force at all if the particle is not moving; if it is moving the force is at right angles to the direction of movement. There's no arrangement of electrical charges that will produce these effects, so it doesn't work to think about the poles of a magnet as if they're charged.

    The force on a particle with charge ##q## moving with velocity ##\vec{v}## in a magnetic field ##\vec{B}## is ##\vec{F}=q\vec{v}\times\vec{B}## where the ##\times## operation is the vector cross-product.

    Google for "Lorentz force" for more information.
     
  6. Aug 18, 2014 #5

    CWatters

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    Heads up: Don't try this with a TV unless you want to ruin it.
     
  7. Aug 18, 2014 #6

    Simon Bridge

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    The magnet is likely interfering with the internal workings of the TV... But, without the reference, it is not possible to be sure.
    It is unlikely that the offered explanation re post no 1 is correct.
    Please provide a link or a reference to the video.
     
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