Which statement about the focusing cup is true?

Which statement about the focusing cup is true?

• A. It emits X-ray photons
• B. It filters low-energy photons
• C. It directs electrons toward the anode focal spot
• D. It is made of lead

Answer: (C)

The focusing cup shapes and directs the electron beam emitted by the filament toward a small, precise spot on the anode. By having a negative potential relative to the filament, the focusing cup creates an electrostatic field that repels off-axis electrons back toward the center, concentrating them at the focal spot. This helps produce a sharp, consistent image by reducing beam spread. It does not emit X-ray photons—the anode interaction does. It also does not filter low-energy photons; filtration is handled by tube filters and design features elsewhere. And it isn’t made of lead—the focusing cup is typically a nickel or similar metal alloy chosen for good thermal and electrical properties and compatibility with the cathode assembly.

The focusing cup shapes and directs the electron beam emitted by the filament toward a small, precise spot on the anode. By having a negative potential relative to the filament, the focusing cup creates an electrostatic field that repels off-axis electrons back toward the center, concentrating them at the focal spot. This helps produce a sharp, consistent image by reducing beam spread.

It does not emit X-ray photons—the anode interaction does. It also does not filter low-energy photons; filtration is handled by tube filters and design features elsewhere. And it isn’t made of lead—the focusing cup is typically a nickel or similar metal alloy chosen for good thermal and electrical properties and compatibility with the cathode assembly.