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. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. The ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism. The International System of Units (SI defines seven dimensionally independent SI base units. André-Marie Ampère (20 January 1775 &ndash 10 June 1836 was a French Physicist and Mathematician who is generally credited as one of the main discoverers Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of

Definition

One ampere is defined to be the constant current which will produce a force of 2×10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical In Geometry, a cross section is the intersection of a body in 2-dimensional space with a line or of a body in 3-dimensional space with a plane etc The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International ^[1][2] For a description of this force law, see Serway. ^[3] See also Ampère's force law. The force of attraction or repulsion between two current-carrying wires (see Figure 1 is often called Ampère's force law. The ampere is a base unit, along with the metre, kelvin, second, mole, candela and the kilogram: it is defined without reference to the quantity of electric charge. The International System of Units (SI defines seven dimensionally independent SI base units. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this The candela (kanˈdɛlə /-ˈdiːlə/ symbol cd) is the SI base unit of Luminous intensity; that is power emitted by a light source in a particular Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

The S. I. unit of charge, the coulomb, is defined to be the quantity of charge displaced by a one ampere per second. The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units ^[4] Conversely, an ampere is one coulomb of charge going past a given point in the duration of one second; that is, in general, charge Q is determined by steady current I flowing per unit time t as:

Realization

The ampere is most accurately realized using a watt balance, but is in practice maintained via Ohm's Law from the units of EMF 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 experimental electromechanical apparatus that may one day provide a definition of the Kilogram based on Electronics. Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance, The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier The quantum Hall effect (or integer quantum Hall effect) is a quantum-mechanical version of the Hall effect, observed in two-dimensional electron systems The official realization of a standard ampere is discussed in NIST Special publication 330 Barry N Taylor (editor) Appendix 2, p. 56.

Proposed future definition

Since a coulomb is approximately equal to 6. 24150948×10¹⁸ elementary charges, one ampere is approximately equivalent to 6. The elementary charge, usually denoted e, is the Electric charge carried by a single Proton, or equivalently the negative of the electric charge carried 24150948×10¹⁸ elementary charges, such as electrons, moving past a boundary in one second. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J

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. A physical Constant is a Physical quantity that is generally believed to be both universal in nature and constant in time One proposed definition of the kilogram is:

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. The elementary charge, usually denoted e, is the Electric charge carried by a single Proton, or equivalently the negative of the electric charge carried 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. The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. This is consistent with the current 2002 CODATA value for the elementary charge which is 1. 60217653×10^-19 ± 0. 00000014×10^-19 C.

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 (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;

See also

• International System of Units
• Ohm's Law
• Hydraulic analogy
• Electric shock
• Ampère's force law
• Ammeter
• Coulomb
• Magnetic constant

References

External links

• The NIST Reference on Constants, Units, and Uncertainty
• A short history of the SI units in electricity
• NIST Definition of ampere and μ₀