A strong electrical voltage is applied across two metal electrodes inside the tube. The negative electrode is the cathode and the positive electrode is the anode. This high voltage pulls negatively charged particles right off the metal cathode.
These particles fly rapidly across the empty vacuum space toward the positive anode. This fast-moving invisible stream of particles is called a cathode ray. The glass tube often contains an inner coating of a chemical called phosphor.
The chemical phosphor glows brightly whenever the fast moving particles crash into it. This fluorescent glow allows scientists to clearly see the path of the invisible beam. Researchers can easily bend this glowing beam using strong magnets or electrically charged plates.
The flying beam will always curve toward a positively charged metal plate. This specific bending behavior proves that the unknown particles carry a negative electrical charge. Students sometimes mistakenly confuse cathode rays with normal light rays.
However, cathode rays have actual mass and respond to magnetic fields. Light rays have no resting mass and ignore magnetic fields completely. For decades, scientists believed atoms were solid spheres that could never be broken.
J. J. Thomson used this tube in 1897 to formally discover the electron.
He proved that atoms actually contain much smaller and lighter pieces. This monumental discovery completely changed how modern chemistry understands atomic structure.