The Coulomb Torsion Balance

The works of Franklin and Dufay, which took place in the mid-18th century, had only qualitative aspects about the electrical phenomena that had been addressed up to that time. With only qualitative aspects, scientists believed that it was not possible to achieve great advances in the studies of electricity, in this sense, they realized the great need to obtain quantitative relationships about the quantities involved in the phenomena electric.
In particular, there was great concern in quantitatively relating the electrical force with the distance between two bodies. Some physicists in the late 18th century realized that there were similarities between electrical attraction and gravitational attraction, so many of them hypothesized that the electrical force could vary with the square of the distance between bodies, as well as the force. gravitational. However, it was necessary to carry out careful measures to verify if this hypothesis was true.
Among all the works that were carried out in order to verify this hypothesis, the experiments stand out carried out by Coulomb who, in the year 1785, made a report on his work and delivered it to the Academy of Sciences of France. Coulomb built a device called

torsion balance, through which he could make measurements of the force of attraction and repulsion between two electrically charged spheres. In this scale built by Coulomb there is a rod that is suspended by a string and at each of its ends there is a sphere. Taking another rod with a sphere also electrified, it makes the approximation between the two. Due to the electrical force that manifests itself in this process, the rod that is suspended by a wire rotates, causing a twist in the wire. By measuring the angle of twist, Coulomb was able to determine the force between the spheres. Another scale very similar to this one was used by Cavendish, at the same time, to prove the Law of Universal Gravitation and measure the value of the gravitation constant G.
After performing several measurements with the spheres separated at various distances, Coulomb ended up conclude that the electrical force was inversely proportional to the square of the distance between the two spheres. Furthermore, he concluded that the electrical force was proportional to the product of the electrical charges of the spheres involved. Due to these conclusions, he ended up arriving at the definitive expression of the law that determines the electrical force between two electrified bodies, an expression that bears his name: Coulomb's Law.
This discovery by Coulomb was very important for the development of the field of electricity, considering that 19th and 20th century numerous advances were made in this area, new studies were made and new laws were discovered.

By Marco Aurélio da Silva
Brazil School Team

Electricity - Physics - Brazil School

Source: Brazil School - https://brasilescola.uol.com.br/fisica/a-balanca-torcao-coulomb.htm