Hall effect

As an electric current flows through an electrical conductor in a magnetic field, the magnetic field exerts a transverse force on the moving charge carriers, providing a tendency for the charge carrier to move to one side of the conductor.

Technical Details
For simple metals, the charge carriers are only electrons, and the Hall Voltage (V->H) is defined by:

$$V_H = IB / ned$$

where I is the current across the plate length, B is the magnetic flux density, d is the depth of the plate, e is the electron charge, and n is the charge carrier density is the electrons.

Applications
Hall Probes are usually used as magnetometers (measurement of magnetic fields). Hall sensors produce a very low signal and therefore tend to need amplification. Hall Effect Sensors typically contain both a Hall Probe and high-gain integrated circuit amplifier.

Hall Probes can be used for measuring magnetic fields, but are typically used as parts of larger sensors, such as high-precision switches and rotation sensors.