The prefix "milli" indicates one thousandth of the base unit it precedes, in this case the ampere. The milliampere has its origins in the ampere. It is defined as one thousandth of an ampere. This definition would also be based on the re-definition of the second which would be defined as the fixed numerical value of cesium frequency.Ī milliampere (symbol: mA) is a submultiple of the SI base unit of electrical current, the ampere. The proposed re-definition of the ampere involves using a fixed numerical value of elementary charge of 1.602176634 × 10-19 when expressed in coulombs. The ampere is one of the units being considered for re-definition due to the difficulty of maintaining high precision in practice. Although the definitions of some units may change, the actual size of the units would remain the same the change in definition will not have much, if any, effect on the daily use of these units.
The International Committee for Weights and Measures (CIPM) has proposed re-definition of some of the SI base units in an attempt to further improve the system. The definition of some SI base units may change in the near future. An ampere can be expressed in the form of watts/volts, or W/V, such that an ampere equals 1 W/V, since power is defined as a product of current and voltage. The current definition of the ampere has been in place since 1948 but may change in the near future.Īs the SI base unit of electric current, the ampere is used worldwide for almost all applications involving electric current. The size of the unit was chosen such that it would fit conveniently within the metre-kilogram-second system of units. In the centimeter-gram-second system of units, the ampere was defined as one tenth of the unit of electrical current of the time, which is now known as the abampere. The ampere is named after Andre-Marie Ampere, a French mathematician and physicist. In terms of the SI unit of charge, the coulomb, one ampere is defined as one coulomb of charge passing through a given point in one second. The ampere is defined formally as the constant current at which a force of 2 × 10 -7 newtons per meter length would be produced between two conductors, where the conductors are parallel, have infinite length, are placed in a vacuum, and have negligible circular cross-sections.
The ampere (symbol: A), often referred to as simply amp, is the base unit of electric current in the International System of Units (SI).
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