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Marconi Museum

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Una macchina elettrostatica è composta da un elemento isolante (cilindro di vetro), da una serie di cuscini, da un tubo di metallo (primo conduttore) e da una manovella. Quando si gira la manovella, i cuscini sfregano contro il vetro e lo elettrizzano per strofinio. Le cariche accumulate sul vetro vengono raccolte da un pettine di metallo collegato al primo conduttore. Le cariche del primo conduttore sono così disponibili per eseguire vari esperimenti.



















Here is the phenomenon that until 1799, year of the invention of Volta's battery, allowed the execution of all electrical experiments. Once upon a time where neither light bulbs, nor electric currents, nor batteries, had already been invented, electrical events had to be “generated” to be observed. Electrical machines had exactly this purpose. During the 7th century electrical experiments were often executed to entertain the audience and instead of pieces of paper, strands of hair were used. They belonged to ladies and, once electrified, they would be lifted. The repertoire of electrifying/thrilling experiments was very wide. During the “electric soiree“ electrical machines were used to produce big sparks which burned alcoholic substances put in special cups, or were used to light up glass tubes where a series of aluminum drops drew long spirals: in darkened rooms these spirals were traversed by a shower of small sparks with guaranteed stage effects. Several theories attempting to give an account of the electrical effects. From the second half of the eighteenth century the accepted theory was that of the "one fluid" by Benjamin Franklin. According to the theory of Franklin each body contains a certain "natural" amount of electric fluid which, thus being in a state of equilibrium, does not show any effect. However, when this state of equilibrium is altered, that is, when in a body occurs an excess or a deficiency of the natural amount of electric fluid, the body becomes electrically charged, respectively, the positive or negative sign. Since the tendency of the electric fluid is at equilibrium, a negatively charged body, placed in the vicinity of a positively charged body, will be attracted to this. The stroke of the electric spark, according to Franklin, comes from the passage of the electric fluid from one body to another and also marks the neutralization of electrical disequilibrium.










Forza elettrostatica (o legge di Coulomb): esprime la forza con cui due cariche elettriche puntiformi poste ad una certa distanza si attraggono o si respingono. Tale forza è direttamente proporzionale al prodotto delle cariche ed inversamente proporzionale al quadrato della distanza. Cariche di segno opposto si attraggono, cariche dello stesso segno si respingono.



Conduttore: un corpo in cui gli elettroni possono muoversi liberamente da una parte all'altra, senza essere legati al nucleo degli atomi.

Isolante: un corpo i cui elettroni non possono muoversi liberamente da una parte all'altra del corpo, essendo legati ai nuclei.

Carica elettrica positiva (negativa): la carica elettrica si misura in Coulomb. Essa è un multiplo intero, positivo o negativo, della carica elettrica elementare, cioè la carica dell'elettrone.



















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