What is emitted by the hot metal filament in a cathode ray oscilloscope?

Explanation

In a cathode ray oscilloscope (CRO), the hot metal filament emits electrons through a process called thermionic emission. When the filament is heated to a high temperature, electrons gain enough energy to escape from the surface of the metal and form a cloud of electrons around it. These emitted electrons are then accelerated and focused into a narrow beam by the electric field within the CRO tube. This electron beam is used to create the visual display on the screen of the CRO by striking a fluorescent coating, producing light that forms the waveform or pattern being analyzed.