If a current I passes through a long, flat bar and if the bar is in a magnetic
field B perpendicular to its large, flat surface, then a voltage UH appears across
the bar, perpendicular to I and B. The Hall voltage UH is easily computed by
considering the electric and magnetic forces on the charge carriers in the bar.
Writing UH = RHI, the Hall resistance RH is found to be RH = B/(ene),
i.e., proportional to the magnetic field B and inversely proportional to the density
ne of the carriers, each having charge e.