Who discovered that cathode rays are made up of electrons

J.J. Thomson discovered cathode rays and Stoney named it electron.

The discovery that cathode rays are composed of electrons is a significant milestone in the history of physics and chemistry. It was J.J. Thomson who, through his experiments in 1897, demonstrated that cathode rays are streams of negatively charged particles, which he later identified as electrons. Thomson used a cathode ray tube and applied both electric and magnetic fields to show that the rays were deflected, proving they carried a negative charge and had mass. This discovery led to the realization that electrons are fundamental subatomic particles present in all atoms.

Although Thomson discovered cathode rays and identified their composition, the term "electron" was coined earlier by George Johnstone Stoney in 1891. Stoney introduced the term to describe the fundamental unit of electric charge, but it was Thomson’s work that provided experimental evidence of the electron’s existence and properties. Together, their contributions laid the foundation for modern atomic theory and the study of subatomic particles.