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Homework Help: Conducting rail ciruit, against gravity

  1. Jun 5, 2010 #1
    1. The problem statement, all variables and given/known data

    So my text book has a lot of example of conducting rails moving horizontally with unknown variables of F and B, but how would you approach a problem that has such a device pointed vertically with the moving bar droping? lets say R and B are known and we need to find I(current) sufficient to counteract gravity so it doesn't accelerate past a velocity required to generate that current.
    2. Relevant equations
    Fb=qv x B
    R = delta V/I
    Fg = mg (call the mass of the rod m )
    I = p/delta V

    3. The attempt at a solution

    I played with it, but not sure if Im right.The part im stuck on is what relation of the magnetic field do I set equal to Fg

    is it Fg= qV x B
  2. jcsd
  3. Jun 5, 2010 #2
    So I found a formula for magnetic levitation that allows me to relate magnetic field strength and gravity

    F= IlB=mg

    if Im right this allows me to determine the current needed to counteract gravity.Does this sound right? Anybody no where that formula is derived from?
  4. Jun 6, 2010 #3
    Can somebody give me some advice here? Its kind of hard to ask questions that aren't in the book, if your unsure of what your doing :rolleyes:
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