Definition:Ampere (Unit)

Definition
The ampere is the SI base unit of electric current.

It is defined as being:


 * The constant current which will produce a force of attraction whose value is $2 \times 10^{–7}$ newtons per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.

This arises from Ampère's Force Law, which states that such an attractive force exists.