One amp is defined as the current producing an attractive force of 2 Ã -- 10 â `` 7 newtons per metre of length between these wires . AmpÃ re 's force law states that there is an attractive force between two parallel wires carrying an electric current . This force is used in the formal definition of the ampere which states that it is `` the constant current which will produce an attractive force of 2 Ã -- 10 â `` 7 newton per metre of length between two straight , parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum '' .