At sufficiently low pressure, a discharge takes place between the two electrodes of a discharge tube on applying an electric field, and a fluorescent glow appears on the glass opposite to the cathode. The cause of this fluorescence was attributed to which of the following?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → the radiation which appeared to be coming from the cathode
The glow appeared on the glass opposite to the cathode, so its cause was traced to rays coming from the cathode. These cathode rays were later shown to be streams of fast moving negatively charged particles.
NCERT (2026-27):
Introduction – “… A fluorescent glow appeared on the glass opposite to cathode. … The cause of this fluorescence was attributed to the radiation which appeared to be coming from the cathode. These cathode rays were discovered, in 1870, by William Crookes who later, in 1879, suggested that these rays consisted of streams of fast moving negatively charged particles.”