# Why is the Ampere a base unit?

• Isaac0427
In summary, according to the proposed redefinition of SI base units, the Ampere will remain a base unit due to its technological and practical importance. Although charge is more fundamental, it is easier and more practical to measure current than charge, especially in real-life and technical applications. Additionally, the amount of charge a battery can energize is an important specification, usually measured in Amp hours.

#### Isaac0427

Just out of curiosity, why is the Ampere a base unit and not the Columb? It seems to me that charge is more fundamental than current. Thanks!

It's easier to measure a current than a charge.

• cabraham
axmls said:
It's easier to measure a current than a charge.

And there are also a number of other reason. One very important property of the base units is that they are technologically/commercially important.. People forget that the SI is mainly a practical system for use in our everyday lives (which is why the Candela is a base unit) ; meaning practical considerations are more important that what is most satisfying from a philosophical point of view.

The re-definition of the SI will see the Ampere (as well as a few other units) be re-defined, but it will still be the base unit for the electrical units,

Ampere is simply related to Coulomb, although not as unity. In a real life and especially in techniques, charge is used to describe static effects, which without strong isolation and shielding are not constant, because of a various forms of leakages. Much easier and cheaper is to stabilize dynamic situation of charge flow, ie electric current measured in Amperes. Additionally, charge flow generates most effects of electrodynamics, including energetic and "electronic" we are surrounded.

zbikraw said:
...charge is used to describe static effects, which without strong isolation and shielding are not constant,
The amount of charge a battery can energize is an important specification. It basically tells you how big the battery is or how long it can last.

David Lewis said:
The amount of charge a battery can energize is an important specification. It basically tells you how big the battery is or how long it can last.

And usually you get this specification in an albeit convoluted form, the "Amp hour", all though on its own this is quite useless, typically you also want to know how many joules you can get out of each of those charges...

If electric charge (the physical quantity) is not used to describe static effects then it's easy to measure. Multiply current by time.

## 1. What is the definition of a base unit in science?

A base unit in science is a fundamental unit of measurement that is used to define other units. These units are considered to be the most basic and important units of measurement and are used to measure physical quantities such as length, time, mass, and electric current.

## 2. Why is the Ampere considered a base unit?

The Ampere is considered a base unit because it is one of the seven base units of the International System of Units (SI). These units are considered to be the most fundamental and universally accepted units of measurement. The Ampere is used to measure electric current, which is a fundamental physical quantity in electromagnetism.

## 3. How is the Ampere defined as a base unit?

The Ampere is defined as the constant current that, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in a vacuum, would produce a force between these conductors of 2 x 10^-7 newtons per meter of length.

## 4. Are all base units universally accepted?

No, not all base units are universally accepted. The International System of Units (SI) is currently the most widely used system of measurement and recognizes seven base units. However, there are other systems of measurement, such as the Imperial system, that use different base units.

## 5. Can base units change over time?

Yes, base units can change over time as our understanding and technology advances. For example, the definition of the meter has changed multiple times since it was first established in 1799. As science and technology continue to evolve, it is possible that the definitions of other base units, including the Ampere, may also change in the future.