Notice that the magnitude of the induced emf and the direction of the current agree
with the results we derived earlier, in the section on motional emf.
This example also shows how a violation of Lenz’s law would lead directly to a
violation of the law of conservation of energy. The current in the sliding rod is
directed upward, as we saw from using Lenz’s law, so the conduction electrons are
drifting downward. The force on these drifting electrons—and thus the rod itself—
is directed to the left, opposing the force that’s pulling the rod to the right. If the
current were directed downward, in violation of Lenz’s law, then the magnetic
force on the rod would be to the right, causing the rod to accelerate to the right with
ever-increasing speed and kinetic energy, without the input of an equal amount of
energy from the outside.