Posted by **lauren** on Thursday, April 15, 2010 at 3:22pm.

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**, Thursday, April 15, 2010 at 3:57pm
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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