The ampere (symbol: A) is the SI base unit of electric current. It is named after André-Marie Ampère, one of the main discoverers of electromagnetism. The SI system of units defines seven SI base units: physical units defined by an operational definition. ... Electric current is the flow of electric charge. ... André-Marie Ampère (January 20, 1775 – 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, encompassing all of space, which exerts a force on those particles that possess the property of electric charge, and is in turn affected by the presence and motion of such particles. ...

Definition

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2×10^–7 newton per metre of length. Cross section may refer to the following In geometry, Cross section is the intersection of a 3-dimensional body with a plane. ... The metre, or meter, is a measure of length. ... The newton (symbol: N) is the SI unit of force. ...

Electric current is the time rate of change or displacement of electric charge. One ampere represents the rate of 1 coulomb of charge per second. Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ... The coulomb (symbol: C) is the SI unit of electric charge. ...

The ampere is defined first (it is a base unit, along with the metre, the second, and the kilogram), without reference to the quantity of charge. The unit of charge, the coulomb, is defined to be the amount of charge displaced by a one ampere current in the time of one second. Look up second in Wiktionary, the free dictionary. ...

Explanation

Because it is a base unit, the definition of the ampere is not tied to any other electrical unit. The definition for the ampere is equivalent to fixing a value of the permeability of vacuum to μ₀ = 4π×10⁻⁷ H/m. Prior to 1948, the so-called "international ampere" was used, defined in terms of the electrolytic deposition rate of silver. The older unit is equal to 0.999 85 A. In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. ... In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Atomic mass 107. ...

The ampere is most accurately realised using an ampere 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 ampere balance (also current balance or Kelvin 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, named after its discoverer Georg Ohm [1], states that the potential difference between two points along a connected path and the current flowing through it are... International danger 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: Ω) 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 systems of electrons subjected to low temperatures and strong magnetic fields, in which the Hall conductance σ takes on the quantized values where e is the elementary charge and h 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. Current (electricity), 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 interactions. ... 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. ... Look up second in Wiktionary, the free dictionary. ... 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. ...

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 through a surface in one second. More precisely, using the accepted 2002 CODATA value of the elementary charge (derived from the Josephson constant and von Klitzing constant, both measured values with non-zero uncertainty), the ampere can be thought of as an electric current approximately equal to 6.24150948×10¹⁸ elementary charges per 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. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... CODATA (Committee on Data for Science and Technology) was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. ... The magnetic flux quantum Φ0 is the quantum of magnetic flux passing through a superconductor. ... The quantum Hall effect is a quantum mechanical version of the Hall effect, observed in two-dimensional systems of electrons subjected to low temperatures and strong magnetic fields, in which the Hall conductance σ takes on the quantized values where e is the elementary charge and h is Plancks...

As with other SI base units, there have been proposals to redefine the kilogram using conventional values (CIPM, 1988, Recommendations 1 and 2, PV, 56, 44-45 and Metrologia, 1989, 26, 69-70) of the von Klitzing constant (R_K-90 = 25 812.807 Ω exactly) and of the Josephson constant (K_J-90 = 483 597.9 GHz/V exactly) . This proposed definition of the kilogram is: Cover of brochure The International System of Units. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ...

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 6.241 509 629 152 65×10¹⁸ elementary charges per second.

This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.602176491612271×10^-19 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6.241 509 629 152 65×10¹⁸ elementary charges and the ampere as being the electrical current of exactly 6.241 509 629 152 65×10¹⁸ elementary charges per second. This is slightly different from but within the standard uncertainty of the current 2002 CODATA value for the elementary charge which is 1.60217653×10^-19 ± 0.00000014×10^-19 C. This is because the 1988 CIPM conventional values for the Josephson and von Klitzing constants are not identical to the 2002 CODATA values. 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. ... In probability and statistics, the standard deviation is the most common measure of statistical dispersion. ...

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.

Image File history File links SI_Brochure_Cover. ... Cover of brochure The International System of Units. ... André-Marie Ampère (January 20, 1775 – 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. ...

See also

• SI
• Ohm's Law
• Electric shock
• Ampere's law

Cover of brochure The International System of Units. ... A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law, named after its discoverer Georg Ohm [1], states that the potential difference between two points along a connected path and the current flowing through it are... 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. ... In physics, Ampères law is the magnetic equivalent of Gausss law, discovered by André-Marie Ampère. ...

External links

• The NIST Reference on Constants, Units, and Uncertainty
• A short history of the SI units in electricity
• @.ampere : Ampère and history of electricity Correspondence, Main books, Movies, 3D VRML - web site create by the CNRS, edited by the Centre de Recherche en Histoire des Sciences et des Techniques : Mme Christine Blondel - CNRS and M. Stéphane Pouyllau - CNRS