# What is Hall Effect

If you ask a person familiar with the physics on the level of a basic knowledge of what a Hall effect and where it is used, you may not receive a response.Surprisingly, in the realities of the modern world this happens quite often.In fact, Hall effect used in many electrical devices.For example, once popular computer floppy disk drives determined the starting position of the motor with a Hall generator.Appropriate sensors are "moved" and in the scheme of modern drives to CDs (both CD, and DVD).Furthermore, applications include not only the various measuring devices, even electrical power generators based on the conversion of heat to the stream of charged particles by a magnetic field (MHD).

Edwin Herbert Hall in 1879, carrying out experiments on a conductive plate, found wanton, at first glance, the phenomenon of occurrence of the potential (voltage), the interaction of the electric current and magnetic field.But first things first.

Let's do a little thought experiment: take a metal plate and pass

an electric current through it.Next, place it in an external magnetic field so that the field intensity lines are oriented perpendicular to the plane of the conductive plate.As a result, at the edges (transverse to the direction of current) potential difference.This is the Hall effect.The reason for its occurrence is known Lorentz force.

There is a way to determine the value of the resultant voltage (sometimes called potential Hall).The general expression takes the form:

Uh = Eh * H,

where H - the thickness of the plate;Eh - strength of the external field.

Since the potential is due to the redistribution of charge carriers in a conductor, he is limited (the process does not continue indefinitely).Lateral movement of the charges cease at the moment when the value of the Lorentz force (F = q * v * B) called with opposition q * Eh (q - charge).

Since the density of the current J is equal to the concentration of the charges, their speed and the unit value of q, then there

J = n * q * v,

respectively,

v = J / (q * n).

Hence (related by the formula of intensity):

Eh = B * (J / (q * n)).

combine all of the above and determine the potential value of the charge through the hall:

Uh = (J * B * H) / n * q).

Hall effect suggests that sometimes in metals is not observed electronic and hole conductivity.For example, it is cadmium, beryllium, and zinc.Studying Hall effect in semiconductors, no one doubted that the charge carriers - the "hole".However, as already indicated, it is also applicable to metals.It was believed that the allocation of charges (capacity building Hall) common vector is formed by electrons (negative).However, it turned out that in the current pose is not electrons.In practice, this property is used to determine the density of charge carriers in the semiconducting material.

No less known quantum Hall effect (1982).He is one of the conduction properties of two-dimensional electron gas (particles can only move freely in both directions) in a very low temperature and high external magnetic fields.In the study of this effect was discovered the existence of "granularity".The impression that the charge is not formed by single carriers (1 + 1 + 1), and component parts (1 + 1 + 0.5).However, it appeared that no laws are violated.In accordance with the Pauli principle, around each electron in a magnetic field is created by a kind of whirlwind of quanta of flux.With the increase in the intensity of the field there is a situation when the line "one electron = one vortex" no longer holds.In every particle there are several magnetic flux quanta.These new particles are precisely the cause of a fractional result in the Hall effect.

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