Fundamental Unit-ampere

Why current is a fundamental unit? Insead of voltage i.e potential diffrence! In case of RC circut the link containg capacitar has no currunt but potential diffrence after compleat charging! So, voltage can exist without current but current without voltage dosent mean! As we know fundamental units never depends any other physical quntity!
- Shubhansu (age 18)
Raebareli, Uttarpradesh, India

Hello Shubhansu,
This is a very intriguing question! The short answer for this question is just a matter of convention.
In the most standard unit system, the International System of Units (SI system,) there are seven base units. Those are

1. meter for length
   
2. kilogram for mass
3. second for time
4. ampere for electric current
5. kelvin for temperature
6. candela for luminous intensity
7. mole for the amount of substance.
   

These units are chosen to be "fundamental" such that all other known physical units can be expressed in terms of the above seven units. One important reason such units are chosen is that back when these units were established these properties were easy to measure. Please notice that by "expressed", we don't mean anything about causality of the physical properties. You are right that in a circuit, current is a consequence of the presence of potential difference and of course with modern technology, other properties also become easier to measure. However the seven units remain unchanged as we become very used to the SI system and are reluctant to change them.

Hope this helps

Lingyi

(published on 02/03/2013)