by James Little (modified by K.M.)

In the Hall effect experiment you take a semiconductor chip that is running a current and put it in a magnetic field perpendicular to the direction of current. Any negative charge carriers in the current will be pulled towards one side of the semiconductor due to the magnetic part of the Lorentz Force, F = q(v x B). An induced charge of positive sign will collect of the opposite side of the chip. This creates a voltage (surprise... the Hall voltage) across the chip which is perpendicular to the direction of both the current and magnetic field.

The magnitude of the Hall voltage is linearly related to the current and magnetic field strength. However, the sign of this voltage is reversed if the charge carriers are positive.

After the magnetic field is applied we use some electronic equipment to measure the sign and density of charge carriers (and a quantity called, fortuitously, the Hall coefficient) for two different semiconductor chips. Sounds simple, well, I'm cutting the explanation short to keep it simple. Believe me the electronics involved make this a non-trivial experiment.

The computer and all the equipment here is set up for the Hall effect lab (Photo by Barb Mattson)

The picture below is donated by Joshua Santarpia and is a plot of the hall voltage vs. the applied B field. The charge density is obtained from the slope of the graph.