We explain who Joseph John Thomson was, what his main contributions to the field of physics were, and which important 20th-century scientists he helped train.
JJ Thomson is one of the most prominent British physicists in history.
Who was Joseph John Thomson?
Joseph John Thomson, also known as JJ Thomson, was a prominent British physicist and mathematiciandiscoverer of the electron and the first atomic isotopes, creator of his own atomic model and winner of the Nobel Prize in Physics in 1906. He was one of the key figures in the development of contemporary physics at the beginning of the 20th century.
In addition to being a prominent researcher, Thomson contributed to the training of an important generation of European and American scientistsamong whom were Ernest Rutherford (1871-1937), Niels Bohr (1885-1962), Geoffrey Ingram Taylor (1886-1975), Paul Langevin (1872-1946), among many other students who passed through his laboratory.
Thomson’s atomic model, known as the “plum pudding model”, revolutionized our understanding of atoms until then and served as the basis for the development of other more precise atomic models, such as the Rutherford model and the Bohr model.
Birth and formative years of Joseph John Thomson
Joseph John Thomson He was born on December 18, 1856 in the town of Cheetham Hill, belonging to Manchester, England.His parents were Joseph James Thomson, a bookseller of Scottish descent, and his wife Emma Swindells, both of whom were members of the liberal middle class. Four years later, the couple had another son, Frederick.
Since he was a child, Joseph showed enormous talent for mathematics and He ended up at Owen’s College when he was just fourteen years old. (now part of the University of Manchester). Two years later, Joseph John’s father died unexpectedly, leaving the family in financial difficulties. His mother was forced to sell the family bookshop and move to a smaller house, leaving barely enough money left for Joseph John to continue his education.
The city of Manchester had at that time a prominent reputation as a centre of scientific knowledge in England. John Dalton (1766-1844) had had his laboratories there and had been replaced in the leadership of the Manchester Literary and Philosophical Society by the physicist James Joule (1818-1889), whom the young Thomson had met through his father.
In that context, Owen’s College was a prestigious institution, with excellent professors, such as the Scottish physicist Balfour Stewart (1828-1887), with whom Thomson began his scientific research.His mastery of mathematics earned him an academic scholarship in the following years that allowed him to enter Trinity College at the University of Cambridge in 1876.
Thomson’s life in Cambridge
Thomson joined the Cavendish Laboratories in Cambridge as a lecturer in 1884.
In 1880, Thomson obtained his degree in mathematics and a place at the famous Cavendish Laboratories, where he received the Adams Prize for his master’s thesis in 1883. There he devoted himself to the study and mathematical description of chemical and physical processes, such as electromagnetism..
Between 1881 and 1884 he published numerous articles on the subject, reviewing the theories on light of the recently deceased James Clerk Maxwell (1831-1879), and later his books Applications of dynamics to physics and chemistry (1888), Notes on recent research in electricity and magnetism (1893) and Elements of the mathematical theory of electricity and magnetism (1895).
In 1884, he was also awarded a professorship, which also led to his entry into the Royal Society. In the following years, Thomson met his future wife, Rose Paget, a young student at Cavendish. The couple married in 1890 and were together for fifty years, during which time they had two children: George and Joan Paget Thomson..
JJ Thomson’s son, George Paget Thomson (1892-1975), was also a prominent British physicist who, following in his father’s footsteps, devoted himself to research. In fact, he also studied at Trinity College, Cambridge, and in 1927, together with the American physicist Clinton Davisson (1881-1958), he received the Nobel Prize in Physics.
Around 1896, Thomson visited Princeton University and gave a series of lectures there on the discharge of electricity through gases, in which he expounded the theories that he published the following year in a book on the subject. Thomson’s studies, as well as those of other young physicists, soon inaugurated a new approach in this scientific discipline..
The discovery of the electron
The discovery of electrons in 1897 opened the door to a new understanding of matter.
At the end of the 19th century, the scientific community invested great efforts in the study of the relationships between energy and matter. The existence of atoms was already known and accepted, but their internal structure and the existence of subatomic particles were unknown.This changed when in 1897 Thomson experimentally demonstrated the existence of electrons.
As early as 1874, the British physicist George Johnstone Stoney (1826-1911) had proposed the existence of a basic particle of electricity, that is, an elementary unit of electric current, which he called electronOn the other hand, thanks to Michael Faraday (1791-1867) electrically charged atoms were known or ions (anions and cations), and there was intensive experimentation with electricity.
In this context, Thomson began his experiments with Crookes tubes, glass devices inside which electricity was studied in a vacuum.To do this, a Lenard ray (nowadays known as a cathode ray, that is, generated by a negative electrode) was made to interact with metal plates that produced an electric field, and thus its behavior was observed.
Thomson noticed that the electric field reacted with the positively charged plates, which demonstrated their corresponding negative charge, while something unexpected prevented it from being absorbed by them. This demonstrated the presence of what he called a “corpuscle”, that is, a mass capable of exerting a certain inertia and which therefore constituted the electric rays.
Thomson set about calculating the charge and mass of these particles, which turned out to be 1000 times smaller and lighter than a hydrogen atom.. Sumasa, however, was constant regardless of the type of atoms involved in the experiment. When they became known, these Thomson “corpuscles” were formally called “electrons.”
Thomson’s atomic model
In 1904 Thomson proposed his atomic model, known as the “pudding with raisins”.
After discovering electrons and verifying their mass and type of charge, Thomson formulated an atomic model that gave meaning to these experiences.It is important to note that neutrons and protons had not yet been discovered, so his model was very simple.
Thomson assumed that atoms were composed of these negatively charged corpuscles that he had just discovered, attached to a larger body that must necessarily have a positive charge of the same intensity, given that atoms do not have a defined electrical charge. This way of imagining it became popular as “pudding with raisins”.
Thomson’s logic, based on the experiences of previous scientists such as William Thomson (1824-1907), known as “Lord Kelvin”, proposed that electrons rotated more or less freely around a positively charged body, and that as they moved away from it they increased their positive charge, being, therefore, attracted again towards the center.
This atomic model was formally proposed by Thomson in 1904, and although it had numerous limitations, it also responded to the most recent experiments in atomic physics..
It was also extremely useful for Thomson’s teaching, especially for his doctoral students Ernest Rutherford (1871-1937) and Niels Bohr (1885-1962), who later proposed their own, more complete atomic models. In fact, Rutherford’s experiments with gold foil sought to test Thomson’s model, but ended up laying the groundwork for a new view of atoms.
The Nobel Prize and other scientific contributions of Thomson
Thomson also discovered mass spectrometry and atomic isotopes.
Thomson’s findings were soon recognized and accepted by the scientific community.. Especially after he gave a series of lectures at Yale University in 1903, where he presented his vision of subatomic particles and the composition of light. Many of his perspectives anticipated the photonic theory of Albert Einstein (1879-1955).
During those years he received numerous awards: the Hodgkins and Hughes medals in 1902, the Nobel Prize in Physics in 1906, and in 1908 he was knighted. In 1912, he was also named to the Order of Merit. That same year, on the other hand, he was appointed director of Trinity College, where he made important administrative contributions and continued his teaching and research work. Seven Nobel Prize winners in Physics were trained under his tutelage..
Although his research was not interrupted by the outbreak of the First World War in 1914, Thomson played an important role in the conduct of scientific research for military purposes. In addition, during those years he made other important discoveries: based on the experiences of the German physicist Wilhelm Wien (1864-1928), he discovered the way to obtain positive rays and used them to formulate the first mass spectrometer in history.
With this apparatus, Thomson wanted to measure the relationship between mass and charge of electrons, but when applying it to different types of atoms he discovered that it could be used to separate atoms according to their mass. Thus, He discovered the existence of atomic isotopes, that is, atomic variants of the same element, which act in a similar way but differ in their mass.The first isotopes detected using this method were neon-20 and neon-22.
These and other experimental results were presented in his main publications of the time: Conduction of electricity through gases (1903), On the structure of the atom (1904), Electricity and matter (1905), Corpuscular theory of matter (1908) and Rays of positive energy (1913).
In the following years, Thomson continued to garner recognition: in 1914 he was awarded the Copley Medal, in 1915 the Albert Medal, in 1922 the Franklin Medal and in 1925 the Faraday Medal.
The death of Joseph John Thomson
Thomson held the position of Warden of Trinity College until his death.
Joseph John Thomson died in Cambridge on 30 August 1940, aged 83.. Until that…