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Encyclopedia > Ampere
Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current.

The ampere, in practice often shortened to amp, (symbol: A) is a unit of electric current, or amount of electric charge per second. The ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism. AmpÃ¨re can refer to: AmpÃ¨re (car) Ampere (unit) AndrÃ©-Marie AmpÃ¨re, one of the main discoverers of electromagnetism Ampere (band) Category: ... Image File history File links Galvanometer. ... Image File history File links Galvanometer. ... Electric current is the flow (movement) of electric charge. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... AndrÃ©-Marie AmpÃ¨re (January 20, 1775 â€“ June 10, 1836), was a French physicist who is generally credited as one of the main discoverers of electromagnetism. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ...

## Contents

The ampere is a constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2×10–7 newton per meter of length.[1] A 3-D view of a beverage-can stove with a cross section in yellow. ... This article is about the unit of length. ... For other uses, see Newton (disambiguation). ...

As a result, electric current is also the time rate of change or displacement of electric charge. One ampere represents the rate of 1 coulomb of charge per second.

$mathrm{1 ,A= 1 frac{,C}{s}} ,$

## Explanation

The ampere is most accurately realized using an watt balance, but is in practice maintained via Ohm's Law from the units of voltage 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. The watt balance is an electromechanical apparatus used for the precise measurement of the SI unit of electric current, the ampere. ... A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Josephson junction array chip developed by NIST as a standard volt. ... The ohm (symbol: Î©) is the SI unit of electric resistance. ... Josephson junctions, first postulated by B. D. Josephson and first made by John Rowell and Philip Anderson, are quantum-mechanical circuit elements of superconducting devices. ... The quantum Hall effect is a quantum-mechanical version of the Hall effect, observed in two-dimensional electron systems subjected to low temperatures and strong magnetic fields, in which the Hall conductance takes on the quantized values where is the elementary charge and is Plancks constant. ...

The unit of electric charge, the coulomb, is defined in terms of the ampere: one coulomb is the amount of electric charge (formerly quantity of electricity) carried in a current of one ampere flowing for one second.[3] Current, then, is the rate at which charge flows through a wire or surface. One ampere of current (I) is equal to a flow of one coulomb of charge (Q) per second of time (t): Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... The coulomb (symbol: C) is the SI unit of electric charge. ... In physics the term quantity of electricity refers to the quantity of electric charge. ... This article is about the unit of time. ... In electricity, current refers to electric current, which is the flow of electric charge. ... The coulomb (symbol: C) is the SI unit of electric charge. ...

$mathrm{I=Q/t} ,$

## Proposed future definition

Since a coulomb is approximately equal to 6.24150948×1018 elementary charges, one ampere is approximately equivalent to 6.24150948×1018 elementary charges, such as electrons, moving past a boundary in one second. The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... For other uses, see Electron (disambiguation). ...

As with other SI base units, there have been proposals to redefine the kilogram in such a way as to define some presently measured physical constants to fixed values. One proposed definition of the kilogram is: Look up si, Si, SI in Wiktionary, the free dictionary. ... â€œKgâ€ redirects here. ... In science, a physical constant is a physical quantity whose numerical value does not change. ...

 “ The kilogram is the mass which would be accelerated at precisely 2×10-7 m/s2 if subjected to the per metre force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 metre apart in vacuum, through which flow a constant current of exactly 6 241 509 479 607 717 888 elementary charges per second. ”

This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.60217653×10-19 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent with the current 2002 CODATA value for the elementary charge which is 1.60217653×10-19 ± 0.00000014×10-19 C. The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... The coulomb (symbol: C) is the SI unit of electric charge. ... The coulomb (symbol: C) is the SI unit of electric charge. ...

### CIPM recommendation

International Committee for Weights and Measures (CIPM) Recommendation 1 (CI-2005): Preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants The International Committee for Weights and Measures is the English name of the ComitÃ© international des poids et mesures (CIPM, sometimes written in English ComitÃ© International des Poids et Mesures). ... â€œKgâ€ redirects here. ... For other uses, see Kelvin (disambiguation). ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...

The International Committee for Weights and Measures (CIPM),

• approve in principle the preparation of new definitions and mises en pratique of the kilogram, the ampere and the kelvin so that if the results of experimental measurements over the next few years are indeed acceptable, all having been agreed with the various Consultative Committees and other relevant bodies, the CIPM can prepare proposals to be put to Member States of the Metre Convention in time for possible adoption by the 24th CGPM in 2011;
• give consideration to the possibility of redefining, at the same time, the mole in terms of a fixed value of the Avogadro constant;
• prepare a Draft Resolution that may be put to the 23rd CGPM in 2007 to alert Member States to these activities;
 This SI unit is named after André-Marie Ampère. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (A). But when an SI unit is spelled out, it should always be written in lowercase (ampere), unless it begins a sentence or is the name "degree Celsius". — Based on The International System of Units, section 5.2.

The General Conference on Weights and Measures is the English name of the ConfÃ©rence gÃ©nÃ©rale des poids et mesures (CGPM, never GCWM). ... The General Conference on Weights and Measures is the English name of the ConfÃ©rence gÃ©nÃ©rale des poids et mesures (CGPM, never GCWM). ... Look up si, Si, SI in Wiktionary, the free dictionary. ... AndrÃ©-Marie AmpÃ¨re (January 20, 1775 â€“ June 10, 1836), was a French physicist who is generally credited as one of the main discoverers of electromagnetism. ... Majuscules or capital letters (in the Roman alphabet: A, B, C, ...) are one type of case in a writing system. ... Minuscule, or lower case, is the smaller form (case) of letters (in the Roman alphabet: a, b, c, ...). Originally alphabets were written entirely in majuscule (capital) letters which were spaced between well-defined upper and lower bounds. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ...

Look up si, Si, SI in Wiktionary, the free dictionary. ... A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i. ... Since electric current is invisible and the processes at play in electronics are often difficult to understand in an intuitive way, it is common to teach electronics using analogies to more common sense objects and processes. ... Sign warning of possible electric shock hazard An electric shock can occur upon contact of a human or animal body with any source of voltage high enough to cause sufficient current flow through the muscles or nerves. ... An electric current produces a magnetic field. ... Wire carrying current to be measured Spring providing restoring force An ammeter is a measuring instrument used to measure the flow of electric current in a circuit. ...

## References

1. ^ Paul M. S. Monk, Physical Chemistry: Understanding our Chemical World, John Wiley and Sons, 2004 online.
2. ^ Robert B. Northrop, Introduction to Instrumentation and Measurements, CRC Press, 1997 online
3. ^ Kuzman Ražnjević, Physical Quantities and the Units of the International System (Si), Begell House Publishers, 1995 online

Results from FactBites:

 Ampere (3459 words) André-Marie Ampere, the son of a Lyon city official, was born in Polemieux-au-Mont-d'Or, near Lyon. In general Ampere's law is similar to Gauss's Law of electric fields, except for the fact that it deals with magnetic fields, and uses a line integral instead of the surface integral used in Gauss's Law. Formerly, the definition involved the force that was produced between parallel wires carrying a current; still earlier, the ampere was defined as a flow of one coulomb per second, where the coulomb (a quantity of electrical charge) was taken as the basic unit.
 Units: A (5441 words) One ampere is the current which, if it's flowing in these conductors, creates between them a force of 0.2 micronewtons per meter of length. One ampere of current results from a potential distribution of one volt per ohm of resistance, or from a power production rate of one watt per volt of potential. The ampere per meter is also the SI unit of "magnetization" in the sense of magnetic dipole moment per unit volume; in this context 1 A/m = 0.001 emu per cubic centimeter.
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