Why Ampere is Not a SI Unit? A Brief Overview

• trust143_raj
In summary, the Ampere is not a SI unit because it is defined in terms of current, which is easier to measure precisely than charge. While it is a base unit in the SI system, it is still a derived unit in practice. Efforts have been made to redefine the Ampere in terms of charge/time or to realize it in terms of time, but these experiments are still in progress.
trust143_raj
Why ampere is not a S.I unit?

The Ampere is even a base unit in the SI.

Sorry i posted the wrong question? I tried to say why Ampere is the basic/fundamental unit although it is derived from charge/time(columb/sec)

Did you try google?

An amp is defined in terms of the current required to achieve a certain force between parallel conductors. Not in terms of Coulomb per sec.

With the notable exception of the kilogram, the SI base units are defined in a way as to make the units independently observable. In SI terminology, the coulomb is a derived unit. The reason is that measuring an ampere is a considerably easier (and more precise) task than is measuring a coulomb.

In the SI unit system current is the fundamental quantity and charge is a derived quantity (1 C = 1 A * 1 s).

The reason is simply that current is easier to measure precisely than charge.

Edit: I see D H was faster than I was

DaleSpam said:
The reason is simply that current is easier to measure precisely than charge.

But it is still a very very difficult experiment if the accuracy is to be good enough. No one has -as far as I know- actually realized the Ampere this is way in quite a while (although I am sure there are a few old setups around).
In the "real world" the Ampere actually a derived unit, calculated from the realization of the Volt (Josephson effect) and the Ohm (quantum hall effect).
One of the big topics in metrology over the past few years has been to come up with a useful current standard, something that would allow us to define current in term of charges/second OR to realize the Ampere in terms of time, the latter would be useful since we can meaure time with higher accuracy than anything else (this is how the Volt is realzied. V=Kj*f, Kj being the Josephson constant adn f the frequency)

1. Why is Ampere not considered a SI unit?

Ampere is not considered a SI unit because it is not a fundamental unit of measurement. The SI system only includes seven base units, which are used to derive all other units. Ampere is a derived unit, meaning it is based on the fundamental unit of charge, the Coulomb.

2. How is Ampere defined?

Ampere is defined as the unit of electric current in the SI system. It is defined as the amount of electric charge that passes through a given cross-section of a conductor per unit of time. This definition is based on the relationship between current, voltage, and resistance, known as Ohm's Law.

3. Why was Ampere chosen as the unit of electric current?

Ampere was chosen as the unit of electric current because it is a practical unit that is easily measured and defined. It is also closely related to the fundamental unit of charge, making it a logical choice for measuring current.

4. Can Ampere be converted to other units of measurement?

Yes, Ampere can be converted to other units of measurement. It can be converted to units such as Coulombs per second, milliamperes, or kiloamperes, depending on the specific application or context.

5. Are there any limitations to using Ampere as a unit of measurement?

One limitation of using Ampere as a unit of measurement is that it is only applicable to electric current. It cannot be used to measure other types of current, such as magnetic or fluid currents. Additionally, like all derived units, it is subject to measurement errors and uncertainties.

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