1827 – France
‘Two current-carrying wires attract each other if their currents are in the same direction, but repel each other if their currents are opposite. The force of attraction or repulsion (magnetic force) is directly proportional to the product of the strengths of the currents and inversely proportional to the square of the distance between them’
Another addition to the succession of ‘inverse-square’ laws begun with NEWTON’s law of universal gravitation.
Ampere had noted that two magnets could affect each other and wondered, given the similarities between electricity and magnetism, what effect two currents would have upon each other. Beginning with electricity run in two parallel wires, he observed that if the currents ran in the same direction, the wires were attracted to each other and if they ran in opposite directions they were repelled.
He experimented with other shapes of wires and generalised that the magnetic effect produced by passing a current in an electric wire is the result of the circular motion of that current. The effect is increased when the wire is coiled. When a bar of soft iron is placed in the coil it becomes a magnet. This is the solenoid, used in devices where mechanical motion is required.
Ampere exploited OERSTED’s work, devising a galvanometer which measured electric current flow via the degree of deflection upon its magnetic needle.
He attempted to interpret all his results mathematically in a bid to find an encompassing explanation for what later became referred to as electromagnetism (Ampere had at that time christened it electrodynamics), resulting in his 1827 definition.
Ampere’s name is commemorated in the SI unit of electric current, the ampere.