Cathode (-) components and function.

• A. Copper target and tungsten stem; converts energy to photons.
• B. Heated tungsten filament and molybdenum cup; releases and focuses electrons.
• C. Glass envelope; provides vacuum.
• D. Power supply; accelerates electrons.

Answer: (B)

The cathode serves as the electron source and beam nondispersion mechanism. The heated tungsten filament emits electrons when current passes through it (thermionic emission), and the surrounding molybdenum cup is kept at a suitable potential to shape and focus that electron cloud into a tight beam directed toward the anode. This combination—filament for electron production plus a focusing cup to direct the electrons—defines the cathode’s role in producing a stable, focused electron stream for X-ray generation. The other options describe parts or functions of the anode, the tube envelope, or the high-voltage supply, which are not the cathode’s job.