Which component is a filament that releases electrons when heated and is negatively charged?

• A. Cathode
• B. Anode
• C. Focusing Cup
• D. Protective Housing

Answer: (A)

Thermionic emission is the idea here: a filament heated to a high temperature releases electrons. The component designed to do that is the cathode. When the filament heats up, electrons gain enough energy to break free from the material, forming a cloud of electrons that are directed toward the anode. The cathode is kept at a lower (often negative) potential so the emitted electrons are attracted toward the positively charged anode, creating the flow of current. The anode’s job is to attract and collect those electrons, not to emit them. The focusing cup helps shape and direct the electron beam but does not itself emit electrons, and the protective housing simply encloses the assembly.