Hans Oersted, Danimarca, 1777-1851

illustrazione di un esperimento di elettromagnetismo

From an antique print.


ritratto di Oersted and a bas relief commemorating the great Oersted, about 1870:

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It is said that Oersted, a philosopher and physicist, discovered almost accidentally (1819) the connection between electricity and magnetism while he was giving a demonstration for his students. Twenty years had passed since the invention of the pile! We can repeat this experiment and show how easy it is today to reproduce this extraordinary fact:

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The law giving the value of the intensity of magnetic induction around the straight electrified wire is that of Biot and Savart:

direzione del campo magnetico di un filo rettilineo percorso da corrente

where μ0 is the magnetic permeability of the vacuum or the air. Induction at a point P lies on a plane perpendicular to the wire and is tangent to the circumference of radius d passing through point P.


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But let’s see if the action is reciprocal: if a current moves a magnet, can a magnet move a current?

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Thus the action is reciprocal. For an expression of the forces in play we must go to Ampere. We shall now see in what other way the idea of “reciprocity” can be interpreted.

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If we now move the wire over the magnet, will we reciprocally have the generation of an electric current?


So the answer is affirmative, even though it came only after another ten years had gone by...

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