A Cathode Ray Tube is a vacuum tube used to produce images in devices like old televisions, computer monitors, and oscilloscopes. It works by producing a beam of electrons and directing it onto a fluorescent screen. Explanation of Each Labeled Part 1. Electron Gun It is the source of electrons. It consists of a cathode (heated filament) and anode. When the cathode is heated, it emits electrons due to thermionic emission. The anode accelerates the electrons into a narrow beam. 2. Beam of Electron