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I feel quite stupid, but I just can't parse the following:

"At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one metre apart"

If the wires are one metre apart, then how are they infinitely long?

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Imagine two identical, parallel wires that are infinitely long. The two wires are spaced one meter apart (still in parallel). When current is passed through the wires they would exert force on each other proportional to current.

The infinitely long part ensures the force is uniform through all parts of the wire.

Hope that helps.

Ah... That makes total sense now - thanks!

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