A thin 2.09 m long copper rod in a uniform
magnetic ﬁeld has a mass of 40.6 g. When
the rod carries a current of 0.229 A directed
perpendicular to the magnetic ﬁeld, it ﬂoats
in the magnetic ﬁeld.
The acceleration of gravity is 9.81 m/s²
.
What is the ﬁeld strength of the magnetic
ﬁeld?
Answer in units of T

Question

anonymous · Answer

The force exerted by a magnetic field perpendicular to a current carrying wire is
$$F = BI L $$
where B is the field strength, I is the current, and L is the length of the wire.  For the wire to float, then that force must be equal to the gravitational force,
$$F = mg$$
therefore
$$BIL = mg \rightarrow B = \frac{mg}{IL} $$

anonymous · Answer

thanks ! does this answer sounds about right? 3635.011965.

anonymous · Answer

nvrm, i wasnt converting the g into kg .. lol but thanks for the help!