# Ampere

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.