Potential difference
Electricity and Magnetism

Volta, the opera singer and the electric pistol

Stories from Physics for 11-14 14-16 IOP RESOURCES

Alessandro Volta made many contributions to science. Most famously, the unit of potential difference is named after him. Volta proposed the fundamental degree, a unit of potential difference based on the ‘electric force’ required to unbalance a disc kept in equilibrium by 12 grains (0.8 g) on an electrostatic balance. The unit Volta defined in this way has been calculated to be equivalent to 13,350 V. His experiments led Volta to propose the relationship that is now usually expressed as Q=CV (where Q is the charge on the plates, C is the capacitance and V the potential difference).

Volta is also well-known for developing the electric pile, the first battery that could supply a continuous current. He published his research on electric piles in 1799 and it is said that he was inspired by a book which described the columns that make up the electric organ of a torpedo fish.

In addition to his electrical research, Volta is credited with the discovery of methane. Following a tip-off from a friend, he collected the gas bubbling off a swamp, found it was combustible and named the gas “inflammable air native of marshes”. He combined his two major discoveries in an electric pistol, which fired projectiles through the ignition of methane with an electric spark.

The electric pistol led Volta to a prescient proposal for communicating over a distance – he imagined, though never carried out, an experiment in which a pistol was fired in Milan by discharging a Leyden jar in Como, 50 km north.

Volta is sometimes cited as the father of the cochlea implant. He performed an experiment in which he placed electrodes in both ears, connected them to a pile (with an estimated EMF of 50 V), and reported hearing “a sound like a boiling viscid fluid”. In further investigations of the effect of electrical stimuli on his senses, he wired his eye and tongue to a prepared piece of frog tissue. Completing the circuit, the frog muscles contracted and he experienced a visual stimulus and a sensation of taste.

Volta’s glittering academic career hid an, at times, tumultuous personal life. In his mid-40s, he had a four-year affair with an opera singer, and proposed marriage, but the singer’s low social status was unacceptable to his religious family. Though he contemplated a secret marriage and resigning his professorship, the engagement was ultimately broken off. He later married the daughter of a local government official and had three sons.

Visitors to Volta’s birthplace, Como, can view a neoclassical temple erected in his honour that houses some of his instruments.


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