ESPERIMENTI INTERATTIVI ED EXHIBIT
ritratto di Arago

Francois Arago, France, 1786-1853
A Daguerrotype of Arago

 

foto di un 'disco di Arago'

And an apparatus dating back to the same period: Arago's Disk. On rotating, the copper disk on the right pulls the horseshoe magnet above it. The phenomenon remained a mystery until Faraday explained it some time around 1831, more than ten years later.

 

foto della targa in ottone con il nome di Arago

For many years Arago worked on the determination of the meridian that passed through Paris, adopted prior to that of Greenwich. In Paris there are still these small brass plates (about 190 of them) fixed to the ground to mark "Arago's meridian".

 

antica stampa che ritrae Arago e Ampere

Arago and Ampere discuss electromagnetic phenomena...

 

primo fotogramma del filmato

A magnetic needle (here it is a strip of tin with two small magnets at the ends) is suspended over a disk of aluminium, a non-magnetic metal. Let's see what happens.

Click on the photo to see the experiment
.

 

This left the natural philosophers of the times dumbfounded for many years. As can easily be imagined, they experimented by replacing the disk with any material that came to mind, even beefsteaks, and in all cases obtained inexplicable results. From Faraday onwards there was no longer any mystery. The explanation lies in the currents induced in the disk by the magnetic field of the needle which generates in the disk a magnetic field that opposes the variation that generated it: see the following.

 

primo fotogramma del filmato

And now another experiment which in a certain sense is complementary to the previous one:


Click on the photo to see the experiment.

 

primo fotogramma del filmato

A fundamental application that arrived more than 160 years later: The rotating magnetic-field motor, invented by Galileo Ferraris: here we see a model:

Click on the photo to see the experiment
.

 


exhibit precedente  exhibit successivo