Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A cathode ray is a stream of electrons observed in vacuum tubes. These rays are emitted from the negative electrode (cathode) when voltage is applied across the electrodes.
5 Must Know Facts For Your Next Test
Cathode rays were crucial in the discovery of the electron by J.J. Thomson in 1897.
They travel in straight lines and can be deflected by electric and magnetic fields.
The behavior of cathode rays led to the development of early atomic models, suggesting atoms have internal structure.
Cathode rays cause certain materials to fluoresce, which was key in their initial observation.
Their properties helped establish that electrons are negatively charged particles.
A subatomic particle with a negative charge found in all atoms and acting as the primary carrier of electricity in solids.
Vacuum Tube: An electronic device controlling electric current through a vacuum; used historically to study cathode rays.
Fluorescence: The emission of light by a substance that has absorbed light or other electromagnetic radiation, often observed when cathode rays strike certain materials.