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## Homework Statement

A straight 2.47 -mm-diameter copper wire can just 'float' horizontally in air because of the force of the Earth's magnetic field B, which is horizontal, perpendicular to the wire, and of magnitude 5 x 10-5 T. What current I does the wire carry? (The density of copper is 8.96 g/cm3).

HELP: The wire feels a downward gravitational force of magnitude mg, where m is mass and g = 9.80 m/s2 is the gravitational field strength near the Earth's surface.

## Homework Equations

F=lIB

Gravitational force=mg

## The Attempt at a Solution

Okay, I know /how/ to do this except for one step. I know that I need to find the force using the equation above. Simple enough, except that I don't know how to find the mass. I know that the mass is the density multipled by the volume. However, I don't know how to find the volume with the information I'm given. If someone could just help me out with that little bit, that would be fantastic!