Sir Joseph John Thomson, also known as J. J. Thomson, was a British physicist and Nobel laureate who is credited with the discovery of the electron. He made this discovery in the late 19th century, during a time when the nature of electricity and matter was still largely unknown and the subject of much scientific investigation.
Thomson's work on the electron began in the 1880s, when he was a professor of physics at the University of Cambridge. At the time, it was known that certain substances, such as metals, could conduct electricity, while others, such as glass, did not. However, the mechanisms behind this behavior were not well understood.
To study this phenomenon, Thomson designed an experiment using a cathode ray tube, a vacuum tube in which a cathode (a negatively charged electrode) and an anode (a positively charged electrode) are separated by a small gap. When a voltage is applied across the electrodes, a beam of cathode rays is produced, which can be detected using a fluorescent screen.
Thomson observed that the cathode rays were deflected when they passed through a magnetic field, and he concluded that they must be charged particles. He also found that the deflection was independent of the type of gas present in the tube, suggesting that the particles were not ions (atoms or molecules that have gained or lost electrons).
Based on these and other observations, Thomson proposed that the cathode rays were composed of tiny, negatively charged particles that he called "corpuscles." He also suggested that these particles were a fundamental constituent of all matter, and that they were much lighter than atoms.
Thomson's discovery of the electron was a major milestone in the development of modern physics, and it laid the foundation for the development of the electron theory of matter. It also opened the door to further research into the nature of electricity and the behavior of charged particles, leading to the development of quantum mechanics and the theory of relativity.
In 1906, Thomson was awarded the Nobel Prize in Physics for his work on the electron, and he is remembered today as one of the most important figures in the history of science.