Ampres discovery

In 1820, André Marie Ampère made the surprising discovery that moving charges produce a new force which is not there when the charges are stationary. This force manifested itself in a very simple experiment where two electric currents were running parallel to each other. Ampère noticed that two current-carrying wires attract each other when the currents are running in the same direction and repel each other when their directions are opposite! There is no force before the currents are switched on, or if current flows in one wire only.

The two wires are electrically neutral whether the current flows or does not flow. Ampère could see no reason why positive and negative charges should not remain delicately balanced at all times, whether moving or stationary. Something happens when charges move — nature has given us yet another law!

André Marie Ampère (1775-1836)

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->-

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Figure 10.11 Parallel currents attract and anti-parallel currents repel.

Figure 10.11 Parallel currents attract and anti-parallel currents repel.

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