1. Boris Skoric: Quantum Hall Effect
The classical Hall effect The Hall effect was discovered by Edwin Hall in 1879. It is well known that a charged particle moving in a magnetic field feels a `Lorentz' force perpendicular to its direction of motion and the magnetic field. As a direct consequence of this Lorentz force, charged particles will accumulate to one side of a wire if you send current through it and hold it still in a (perpendicular) magnetic field. This is called the Hall effect. The voltage drop at right angles to the current is called the Hall voltage; The current divided by the Hall voltage is called the Hall conductance. The Hall effect can be put to use in several ways. One application is magnetic field strength measurement. Since the Hall voltage is proportional to the current and the field strength, sending a known current through a medium and measuring the Hall voltage tells you the field strength. Another nice thing is that you can reveal the nature of the mobile charges in a current-carrying medium. The Lorentz force will push a moving hole (positive charge) and a moving electron (negative charge) in exactly the same direction, since they travel in opposite ways; from the sign of the Hall voltage you can tell if there are more mobile holes than electrons or vice versa.

2. Hall Effect -- from Eric Weisstein s World of Physics
When electrons (or holes) move in a conducting plate that is immersed in a magnetic field, they experience a Lorentz force (1) (in MKS), where q is the charge, E is the electric field, v is the velocity, and B is the magnetic field. Note that the second term is transverse to velocity and to the magnetic field. Therefore, if sensing electrodes are placed across the transverse dimension of the plate, a voltage, called the Hall voltage, will appear. Ignoring scattering, and for an ideal plate geometry, the Hall voltage can be written in terms of the current as (2) where I is the current (in amps), B is the magnitude of the magnetic field (in tesla) component transverse to the current, the carriers have charge q (in Coulombs), n is the number density of charge carriers (in ), t is the thickness of the plate (in meters), and (3) is the Hall coefficient, measured in .

3. Hall Effect Measurements
The history of the Hall effect begins in 1879 when Edwin H. Hall discovered that a small transverse voltage appeared across a current-carrying thin metal strip in an applied magnetic field. Until that time, electrical measurements provided only the carrier density-mobility product, and the separation of these two important physical quantities had to rely on other difficult measurements. The discovery of the Hall effect removed this difficulty. Development of the technique has since led to a mature and practical tool, which today is used routinely for testing the electrical properties and quality of almost all of the semiconductor materials used by industry.

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