A horizontal length of current-carrying wire is suspended from
two identical flexible leads that are under tension due to the
weight of the wire. The wire is oriented at right angles to a
uniform magnetic field that has a magnitude of 4 T and is directed
out of the screen of the figure. The length L of the wire is 5 cm
and its mass m is 10 g. What current will produce a magnetic force
on the wire that is just sufficient to remove the tension in the
flexible leads, and which way is the current flowing through the
wire?