physics
posted by lauren .
A thin cylinder of copper has a mass m=50g and is 1 meter long. what is the minimum current that has to flow through the cylinder for it to levitate in a magnetic field of 0.1T.
would i use B=uI/2pi(d)
im confused about what d is and how the mass relates to this...

physics 
drwls
No, that is not the formula to use. That is the formula for the B field produced by the wire.
The magnetic force, B I L, must equal the weight. This assumes the current and horizontal B field are perpendicular and in the right direction to produce an upward force.
M g = B I L
I = Mg/(BL) = 0.05 kg/(0.1T*1m) = 0.5 Amps
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