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Magnetic pinches and MHD

  1. Jan 3, 2010 #1
    Can someone give me an intuitive explanation why plasmas or conductive fluids tend to follow magnetic flux lines?

    E.g. http://en.wikipedia.org/wiki/Magnetohydrodynamics" [Broken] entry on this says:

    If I take a stab at a qualitative explanation, is it because magnetic flux lines are equipotential lines, therefore if the conductor deviates from the flux lines, induced currents are produced which oppose the motion in accordance with Lenz's law?

    Also, I know the explanation for Lenz's law is conservation of energy, but it just seems odd that induced currents so happen to be set up to precisely keep energy conserved.

    What causes magnetic pinching, e.g. in lightning bolts or even lightning rods (below) then? I would have thought an axial current along a conductive fluid would cause charged particles within it to follow a circular orbit. Where do they get the centripetal force to both follow such an orbit, and in fact exceed that for a stable orbit, and end up reducing their orbital radii?

    http://upload.wikimedia.org/wikipedia/en/7/77/Crushed_rod_pollock_barraclough.jpg [Broken]​
    Last edited by a moderator: May 4, 2017
  2. jcsd
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