Hall effect

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The Hall Effect (discovered by Dr. Edwin Hall in 1879) states that when a magnetic field is applied perpendicular to a thin sheet of conducting or semiconducting material through which current is flowing (the Hall element), a potential (voltage) difference will be created on opposite edges of the hall element. By measuring the Hall voltage across the sensing element, one can determine the strength of the magnetic field applied perpendicular to the Hall element. Hall Effect Sensors are readily available from a number of different manufacturers. The most common types are Analog Hall Effect Sensors (which output a voltage that is proportional to the applied magnetic field) and Digital Hall Effect Sensors (which are often used as magnetically controlled switches -- they turn on or off when the applied magnetic field reaches a certain level).

One important feature of tha Hall effect is that it differentiates between positive charges moving in one direction versus negative charges moving in the opposite. The hall effect offered the first real proof that electric currents in metals are carried by moving electrons, and not protons. Interestingly enough, the Hall effect also showed that in some substances (especially semiconductors), it is more appropriate to think of the current as positive "holes" moving rather than negative electrons.