# Ampere

AmAampamperesampsmilliamperemicroamperemilliampcurrentmegaampere
The ampere ( or (UK), symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI).wikipedia
597 Related Articles

### Electric current

currentelectrical currentcurrents
The ampere ( or (UK), symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI).
The SI unit of electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second.

### International System of Units

SISI unitsSI unit
The ampere ( or (UK), symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI).

### SI base unit

base unitSI base unitsbase units
The ampere ( or (UK), symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI).
The units and their physical quantities are the second for time, the metre for measurement of length, the kilogram for mass, the ampere for electric current, the kelvin for temperature, the mole for amount of substance, and the candela for luminous intensity.

### André-Marie Ampère

AmpèreAmpereAmpère, André-Marie
It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics.
The SI unit of measurement of electric current, the ampere, is named after him.

### 2019 redefinition of the SI base units

2019 redefinition of SI base unitsredefinitionredefinition of the SI base units
New definitions, in terms of invariant constants of nature, specifically the elementary charge, took effect on 20 May 2019.
In the redefinition, four of the seven SI base units – the kilogram, ampere, kelvin, and mole – were redefined by setting exact numerical values for the Planck constant (''

### Coulomb

CPicoCoulomBExacoulomb
The ampere was then defined as one coulomb of charge per second.
It is the charge (symbol: Q or q) transported by a constant current of one ampere in one second:

### Joule

JkJMJ
The relation of the ampere (C/s) to the coulomb is the same as that of the watt (J/s) to the joule.
It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.

### Watt

kWMWmegawatt
The relation of the ampere (C/s) to the coulomb is the same as that of the watt (J/s) to the joule.
In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit).

### Electric charge

chargeelectrical chargecharged
The earlier [[Centimetre gram second system of units#Derivation of CGS units in electromagnetism|CGS measurement system]] had two different definitions of current, one essentially the same as the SI's and the other using electric charge as the base unit, with the unit of charge defined by measuring the force between two charged metal plates.
The coulomb is defined as the quantity of charge that passes through the cross section of an electrical conductor carrying one ampere for one second.

### Electric battery

batterybatteriesBattery (electricity)
Constant, instantaneous and average current are expressed in amperes (as in "the charging current is 1.2 A") and the charge accumulated (or passed through a circuit) over a period of time is expressed in coulombs (as in "the battery charge is 30000 C").
A common application is the modern car battery, which can, in general, deliver a peak current of 450 amperes.

### International Exposition of Electricity

International Exposition of Electricity, ParisExposition internationale d'Électricité1881 International Electricity Exposition
In recognition of Ampère's contributions to the creation of modern electrical science, an international convention, signed at the 1881 International Exposition of Electricity, established the ampere as a standard unit of electrical measurement for electric current.
As part of the exhibition, the first International Congress of Electricians presented numerous scientific and technical papers, including definitions of the standard practical units volt, ohm and ampere.

### Abampere

Bibiot
That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart.
One abampere is equal to ten amperes in the SI system of units.

### Multimeter

digital multimeterdigital multimetersDMM
Current can be measured by a multimeter, a device that can measure electrical voltage, current, and resistance.
Macadie invented an instrument which could measure amperes (amps), volts and ohms, so the multifunctional meter was then named Avometer.

### Ohm's law

ohmicOhmohmic losses
The standard ampere is most accurately realized using a Kibble balance, but is in practice maintained via Ohm's law from the units of electromotive force 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.
is the current through the conductor in units of amperes, V is the voltage measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms.

### Centimetre–gram–second system of units

CGScgs unitsCGS unit
The earlier [[Centimetre gram second system of units#Derivation of CGS units in electromagnetism|CGS measurement system]] had two different definitions of current, one essentially the same as the SI's and the other using electric charge as the base unit, with the unit of charge defined by measuring the force between two charged metal plates.
(This approach was eventually used to define the SI unit of ampere as well).

### Volt

VkVvolts
The standard ampere is most accurately realized using a Kibble balance, but is in practice maintained via Ohm's law from the units of electromotive force 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.
One volt is defined as the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points.

### Ohm

Ωohmsmegohm
The standard ampere is most accurately realized using a Kibble balance, but is in practice maintained via Ohm's law from the units of electromotive force 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 ohm is defined as an electrical resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force.

### Ammeter

microammetermoving coil meterampere-meter
Electric currents are measured in amperes (A), hence the name.

### Electromagnetism

electromagneticelectrodynamicselectromagnetic force
It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics.

### Orders of magnitude (current)

3.4789
To help compare different orders of magnitude, the following list describes various ampere levels.

### Hydraulic analogy

drain-pipe theoryelectronic–hydraulic analogelectronic–hydraulic analogy
Usually measured in amperes.

### Electrical injury

electric shockelectrocutionelectrocuted
A person can feel at least 1 mA (rms) of AC at 60 Hz, while at least 5 mA for DC.

### Vacuum permeability

magnetic constantpermeability of free spacepermeability of vacuum
The ampere was that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 newton per meter of length.

### Ampacity

current ratingcurrent-carrying capacitycurrent ratings
e.g. The United States National Electrical Code, Table 310.15(B)(16), specifies that up to three 8 AWG copper wires having a common insulating material (THWN) in a raceway, cable, or direct burial has an ampacity of 50 A when the ambient air is 30 °C, the conductor surface temperature allowed to be 75 °C.

### Clipping (morphology)

clippingclippedclipped form
The ampere ( or (UK), symbol: A), often shortened to "amp", is the base unit of electric current in the International System of Units (SI).