The standard ampere is most accurately realized using a watt balance, but is in practice maintained via Ohm's Law from the units of electromotive force and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively.

In a similar way, accurate AC / DC non-contact ammeters have been constructed using Hall effect magnetic field sensors.

This phenomenon arising due to the nature of charge carriers in the conductor came to be known as the Hall effect, but it was not properly explained at the time, since the electron was experimentally discovered 18 years later.

The quantum Hall effect was discovered by Klaus von Klitzing in 1980 when he observed the Hall conductivity to be integer multiples of a fundamental constant.

Shortly after, in 1982, Störmer and Tsui observed the fractional quantum Hall effect where the conductivity was now a rational multiple of a constant.

The study of topological properties of the fractional Hall effect remains an active field of research.

Devices used for this include Hall effect sensors, current clamps, current transformers, and Rogowski coils.

* Hall effect current sensor transducers

In some contexts it is meaningful to speak of fractions of a charge ; for example in the charging of a capacitor, or in the fractional quantum Hall effect.

The quasiparticles of the fractional quantum Hall effect are also known as composite fermions, which are electrons with an even number of quantized vortices attached to them.

The Hall effect is the production of a voltage difference ( the Hall voltage ) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current.

The Hall effect was discovered in 1879 by Edwin Herbert Hall while he was working on his doctoral degree at Johns Hopkins University in Baltimore, Maryland.

The Hall effect is due to the nature of the current in a conductor.

This cannot explain the opposite sign of the Hall effect observed.

As a result, the Hall effect is very useful as a means to measure either the carrier density or the magnetic field.

One very important feature of the Hall effect is that it differentiates between positive charges moving in one direction and negative charges moving in the opposite.

The Hall effect offered the first real proof that electric currents in metals are carried by moving electrons, not by protons.

The Hall effect also showed that in some substances ( especially p-type semiconductors ), it is more appropriate to think of the current as positive " holes " moving rather than negative electrons.

The sample inhomogeneity might result in spurious sign of the Hall effect, even in ideal van der Pauw configuration of electrodes.

For example, positive Hall effect was observed in evidently n-type semiconductors.

The Hall effect in an ionized gas ( plasma ) is significantly different from the Hall effect in solids ( where the Hall parameter is always very inferior to unity ).

Hall effect devices produce a very low signal level and thus require amplification.

Many devices now sold as Hall effect sensors in fact contain both the sensor as described above plus a high gain integrated circuit ( IC ) amplifier in a single package.

Hall effect devices when appropriately packaged are immune to dust, dirt, mud, and water.

These characteristics make Hall effect devices better for position sensing than alternative means such as optical and electromechanical sensing.

A quantum spin Hall state is a theoretical phase that may pave the way for the development of electronic devices that dissipate less energy and generate less heat.

The College's Hall has a fine hammerbeam-roof, painted in black and gold and decorated with the armorial devices of its benefactors.

The most common magnetic sensing devices are solid-state Hall effect sensors.

In July 2001, Romero and Hall founded Monkeystone Games in order to develop and publish games for mobile devices, and Monkeystone released 15 games ( approximately ) during its short lifespan of three and a half years.

The ' Engine Hall ' exhibits engines of various automobiles, machines used in industry, a jet aircraft engine, and other mechanical devices.

Some parks have been identified as potential targets for terrorist attacks and in these areas, such as the Gateway Arch, Independence Hall and parts of Boston National Historic Park, guards may screen visitors using magnetometers and x-ray devices.

gases ( 2DEG ) in graphite layers and the Quantum Hall effect system in MOSFET type devices,

* John Mauchly, computer pioneer and creator of the ENIAC: While Professor of Physics at Ursinus from 1933 to 1941, developed and tested digital electronic calculating devices at Ursinus's science labs in Pfahler Hall, a building which still stands on campus ( see Gallery, below )

In May 2006, Potter accused the FBI of attempting to recruit an informant within the Portland city offices, going so far as to have his City Hall offices searched for listening devices.

Examples of devices that can provide this isolation are Hall effect current sensors and current transformers ( see clamp meters ).

Current shunts are considered more accurate and cheaper than Hall effect devices.

The Hall briefly consider sending a rescue party, but conclude they have neither the time nor the resources to achieve it ; the unspoken implication is that they consider Elaida's predicament to be a product of her own mistakes and that they are quite content to leave her to her own devices for the time being.

* One or more feedback sensors such as optical encoders, resolvers or Hall effect devices to return the position or velocity of the actuator to the motion controller in order to close the position or velocity control loops.

Photos of Conference Rooms and the General Assembly Hall can be made when these rooms are not being used for meetings.

Originally used in Baker House to signify the Ivy League university tradition, on his return to Finland Aalto used it in a number of key buildings, in particular, in several of the buildings in the new Helsinki University of Technology campus ( starting in 1950 ), Säynatsalo Town Hall ( 1952 ), Helsinki Pensions Institute ( 1954 ), Helsinki House of Culture ( 1958 ), as well as in his own summer house, the so-called Experimental House in Muuratsalo ( 1957 ).

Emmerson Hall, built in 1913, is particularly interesting for the variety of building stones used.

A large wrecking ball was used to demolish Throop Hall, and smashing the concrete revealed massive amounts of rebar, far in excess of safety requirements.

For her job in Duluth, Minnesota, Hall used her musical and poetic talents in an advertising campaign.

He used his zoopraxiscope to show his moving pictures to a paying public, making the Hall the first commercial film theater.

Monzie Square ( named after the Cameron Campbells of Monzie, Perthshire, former landowners in the town ), Station Square, where the long-since demolished railway station used to be, Gordon Square ( named for the Gordons, who owned land where the town now stands in the late 18th century, during which time the town was named Gordonsburgh ), and Cameron Square — formerly known as Town Hall Square.

The Victoria Hall is used for classical music concerts.

One can walk towards Galileo Hall and see the warts ( especially those near the entrances of buildings ) being used as racks for unicycles and skateboards.

Hall probes are often used as magnetometers, i. e. to measure magnetic fields, or inspect materials ( such as tubing or pipelines ) using the principles of magnetic flux leakage.

Also, as Hall voltage is often on the order of millivolts, the output from this type of sensor cannot be used to directly drive actuators but instead must be amplified by a transistor-based circuit.

Hall effect sensors are readily available from a number of different manufacturers, and may be used in various sensors such as rotating speed sensors ( bicycle wheels, gear-teeth, automotive speedometers, electronic ignition systems ), fluid flow sensors, current sensors, and pressure sensors.

) the Hall effect sensor is used as a direct replacement for the mechanical breaker points used in earlier automotive applications.

A Hall effect thruster ( HET ) is a relatively low power device that is used to propel some spacecraft, once they get into orbit or farther out into space.

A radial magnetic field established by magnets on the thruster is used to trap electrons which then orbit and create an electric field due to the Hall effect.

The Corbino effect is a phenomenon involving the Hall effect, but a disc-shaped metal sample is used in place of a rectangular one.

" Locksley " becomes Robin Hood's title in the Scott novel, and it has been used ever since to refer to the fictional outlaw, most notably by Tennyson in his poem, " Locksley Hall ".

Most recently, James Madison University has used funds to create a new baseball and softball field complex by Memorial Hall.

The Mitchell Hall, built 1896, was donated to the community by Alexander Mitchell Farmer at Redwells Farm. Alexander also donated the first Parish Church organ. The Mitchell Hall is used by local community groups, and is an asset to the wider Fife community.

Crystals of LaB < sub > 6 </ sub > are used in high brightness, extended life, thermionic electron emission sources for electron microscopes and Hall effect thrusters.