The Ampere [ ampɛɐ̯ ] with unit symbols, named after the French physicist André -Marie Ampère, is the SI base unit of electric current, while the derived SI unit size "magnetic flux ". While writing the last name of the eponym " amp " with grave accent, the SI unit in the German and English-speaking countries is usually without accent, or " amps " written.

With the definition of amperes in the SI unit system at the same time the magnetic field constant μ0 determined, which is also referred to as a (magnetic) permeability of the vacuum.

History of the definition

If one were to measure current with a derived unit, as happens for example when the CGS system of units, then the electrical quantities by the base units could be expressed only with non-integer exponents. To avoid this, the unit of current was proposed in 1939 as a further base unit.

Historical definition of the German Empire

The law relating to the electrical units of 1 June 1898, 1 ampere is defined as the strength of that current flowing in one second, 1.118 mg of silver deposited from a silver nitrate solution by electrolysis. On this definition, Ampere has been designated later as an international amp; the remaining basic units compatible with the other hand as an absolute amperes.

Current definition

Since 1948, the ampere is defined as follows on each other via the Lorentz force of two conductors:

One ampere represents a flow of one coulomb per second through the conductor cross section:

This represents a rate of 6.24151 · 1018 ( about 6 trillion ) electrons per second.

Suggestions for future definition

In October 2005, the International Committee of the preparations decided on Weights and Measures ( CIPM ) for a redefinition of the units kilogram, ampere, kelvin and mole to meet, based on natural constants in order to decide this at the next General Conference in 2011 can. Thereupon a proposal for the implementation was released in 2006. According to this proposal, the ampere was defined by the flow of a certain amount of particles of the electron charge per unit time.