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    Imagine a rectangular loop floating within mid-air. The top portion of this loop is within a region of uniform magnetic field going in to the page. Obviously if a current goes through this loop then it will experience a force F = BIL where L is the length of the top portion of the rectangular loop. In this case the force experienced is upwards so that the force is greater than gravity and the loop rises upwards. The minimal current need for this is  I = \frac {mg}{BL}

    If we consider a single charge within the loop while it is rising, it has a horizontal velocity component (i.e. just its velocity with the current flow) and vertical component (caused by the magnetic field). I've said that the charges pushing against the surface of the loop is what causes it to rise upwards. A magnetic field is generated by each component of the charge's velocity - I'm assuming that these magnetic field have a similar pattern as a long wire (i.e. circular fields).

    Now my question asks me, by considering the velocity components and magnetic fields produced by the moving charges, what must be supplied to each charge in order to keep the current of the wire at a steady value.

    What the bloody hell is it on about? Can anyone relate to me what it might be suggesting? I don't even see why the current wouldn't be steady?
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Updated: April 7, 2011

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