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Current-carrying conductors placed adjacent to one another will experience a force. The moving charges in the different conductors produce magnetic fields which interact with each other to produce these force(s).

Ampere’s law describes the relationship between current, distance and force between two current-carrying conductors. Use the right-hand grip rule (see right) to determine the direction of the induced magnetic fields. Remember that same-direction fields repel while opposites attract.

\frac{F}{l}=\frac{\mu _0}{2\pi} \frac{I_1 I_2}{d}

*μ*= the magnetic permeability constant_{0}*l*= the common length of the parallel conductors

The Ampere was defined in 1954 using Ampere’s law. The official definition was as follows:

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible cross-section, and placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2 \times 10^{-7}[\katex] newton per metre of length.