Malcolm Rivera
The ampere (often shortened to amp), is the unit of electric current in the International System of Units (SI). One ampere is equal to one coulomb (C) moving past a point per second. In 2019, the SI was revised, and the ampere was defined by fixing the elementary charge e to be exactly 1.602176634×10^-19 C, meaning an ampere is an electric current equivalent to 1019 elementary charges moving every 1.602176634 seconds. This revision replaced the previous definition, which was based on the force between two parallel wires. The ampere is a fundamental quantity in the SI, along with length, mass, time, temperature, and electric current.
| Characteristics | Values |
|---|---|
| SI base units | kilogram, kelvin, ampere, mole, candela |
| Fundamental physical quantities | Length, mass, time, temperature, electric current, amount of substance, luminous intensity |
| Fundamental physical quantities examples | Meter, kilogram, second, Kelvin, Ampere |
| Ampere definition | Current in which one coulomb of charge travels across a given point in 1 second |
| Elementary charge (e) | 1.602176634×10^-19 C |
| One ampere | 1019 elementary charges moving every 1.602176634 seconds, or approximately 6.241509074×1018 elementary charges moving in a second |
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Coulombs per second
The ampere (A), the SI base unit of electric current, is defined in terms of the fundamental physical constant known as the elementary charge (e). This is the amount of electric charge in a single electron or proton. The ampere is a measure of the amount of electric charge in motion per unit time, or electric current. The quantity of electric charge, whether in motion or not, is expressed by the SI unit coulomb (C).
One coulomb is approximately 6.241 x 10^18 electric charges (e). One ampere is the current in which one coulomb of charge travels across a given point in one second. This can be expressed as coulombs per second (C/s).
The relationship between the ampere and the coulomb is similar to that of the watt (W) and the joule (J). The watt is a unit of power, which is the product of current and voltage, and is expressed as W = J/s.
The coulomb is defined as "the quantity of electricity carried in 1 second by a current of 1 ampere". This definition has been in place since the 2019 revision of the SI, which fixed the numerical value of the elementary charge e to be 1.602176634 x 10^-19 C. This means that an ampere is an electric current equivalent to approximately 6.241509074 x 10^18 elementary charges moving in a second.
Prior to the 2019 redefinition, the ampere was defined in terms of the force between parallel, current-carrying conductors. This definition was based on Ampère's force law, which states that there is an attractive or repulsive force between two parallel wires carrying an electric current.
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Electric charge
In the context of electric current, the movement of electric charge is what constitutes the current. This flow of electric charge occurs when there is a difference in voltage, creating a potential difference. Electrons, which carry negative charges, move from lower to higher electrical potential in metallic solids. In other materials, such as semiconductors, the charge carriers can be positive or negative ions, depending on the dopant used.
The electric charge is measured in coulombs (C) in the International System of Units (SI). One coulomb is approximately equal to 6.241 x 10^18 electric charges (e). This means that a single elementary charge (e) is incredibly small, about a tenth of a billionth of the amount of charge in a current of 1 ampere that moves past a point in one second.
The relationship between electric charge and electric current, which is measured in amperes (A), is important to understand. One ampere is defined as one coulomb of electric charge moving past a point per second. In other words, it is the rate of flow of fundamental charges. This definition of an ampere is based on the elementary charge (e), which is the amount of electric charge in a single electron or proton.
The definition of an ampere has evolved over time. Prior to the 2019 revision of the SI system, the ampere was defined in terms of the force between parallel, current-carrying conductors. However, the new definition is solely based on the elementary charge (e), providing a clearer and more precise understanding of electric current.
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Time
The 2019 revision of the SI system set the elementary charge (e) as the basis for defining the ampere. This charge, representing the amount of electric charge in a single electron or proton, was fixed at 1.602176634 x 10^-19 coulombs (C). As a result, one ampere is now defined as the electric current created by approximately 6.241509074 x 10^18 elementary charges moving in one second.
This definition highlights the relationship between electric current and time. One coulomb, which is the SI unit of electric charge, is defined as the quantity of electricity carried in one second by a current of one ampere. In other words, one ampere is equal to one coulomb of electric charge moving past a point in one second.
The connection between the ampere, coulomb, and time is further illustrated by the formula A = C/s, where A represents amperes, C represents coulombs, and s represents seconds. This formula demonstrates that one ampere is indeed dependent on the rate at which electric charge flows over time.
It is worth noting that, prior to the 2019 revision, the ampere was defined differently. It was based on the force between two parallel wires carrying current, rather than the elementary charge. However, the new definition provides a more rational basis for the ampere, even though it presents challenges for measurement due to the extremely small value of e.
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Force between parallel wires
The ampere (A), often shortened to amp, is the unit of electric current in the International System of Units (SI). One ampere is equal to one coulomb (C) of electric charge moving past a given point per second. The ampere is a familiar and indispensable quantity in everyday life. It is used to specify the flow of electricity in hair dryers, extension cords, home circuit breakers, and more.
The ampere has been an internationally recognised unit since 1908 and has been measured with progressively better accuracy over time. The 2019 revision of the SI defined the ampere by taking the fixed numerical value of the elementary charge e to be 1.602176634 x 10^-19 C, which means an ampere is an electric current equivalent to 10^19 elementary charges moving every 1.602176634 seconds, or approximately 6.241509074 x 10^18 elementary charges moving in a second.
Prior to the 2019 redefinition, the ampere was defined as the current passing through two parallel wires one metre apart that produce a magnetic force of 2 x 10^-7 newtons per metre of length. This definition of the ampere was most accurately realised using a Kibble balance, but in practice, the unit was maintained via Ohm's law from the units of electromotive force and resistance, the volt and the ohm.
Ampère's force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force was used in the formal definition of the ampere, giving the vacuum magnetic permeability (magnetic constant, μ0) a value of exactly 4π x 10^-7 henries per metre (H/m, equivalent to N/A^2). The SI unit of charge, the coulomb, was then defined as "the quantity of electricity carried in 1 second by a current of 1 ampere".
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Length
The SI base units for these seven fundamental quantities are the metre (m), kilogram (kg), second (s), kelvin (K), ampere (A), mole (mol), and candela (cd), respectively.
The metre is the SI base unit of length. It is defined as the distance travelled by light in a vacuum in 1/299,792,458 of a second. This definition is based on the speed of light, which is a fundamental constant of nature.
The metre is used to measure not only length but also distance, height, width, depth, and size. It is also used to define other units, such as the newton (N), which is defined as the force required to accelerate one kilogram of mass by one metre per second squared (m/s^2).
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Frequently asked questions
1 ampere (A) is the SI base unit of electric current. It is defined as the flow of 1 coulomb (C) of electric charge per second.
Prior to 2019, the ampere was defined as the current passing through two parallel wires placed 1 metre apart that produces a magnetic force of 2×10^-7 newtons per metre. In 2019, the definition was changed to be based on the elementary charge (e), which is the amount of electric charge in a single electron or proton. The elementary charge was fixed at exactly 1.602176634×10^-19 coulombs, so 1 ampere is now defined as approximately 6.241509074×10^18 elementary charges moving in 1 second.
The fundamental quantities that constitute 1 ampere are length, mass, time, temperature, and electric current. These are measured in meters, kilograms, seconds, kelvin, and amperes, respectively.
