Which sequence correctly describes how an X-ray is produced in the tube?

• A. Electrons are emitted at the cathode, collide with the anode, producing X-rays
• B. X-rays pre-exist in the glass envelope and radiate when heated
• C. Electrons travel from anode to cathode without collisions
• D. The filament directly emits X-rays when heated

Answer: (A)

The main idea is how X-rays are produced in an X-ray tube: electrons are released from the heated cathode (thermionic emission), are accelerated toward the anode by the high voltage, and when they strike the anode target their energy is converted into X-ray photons (with some energy turning into heat). This description—electrons emitted at the cathode, collide with the anode, producing X-rays—fits the actual process precisely. X-rays aren’t pre-existing in the glass envelope, and heating the filament doesn’t emit X-rays directly; the filament’s job is to emit electrons, which then produce X-rays upon hitting the target. Also, electrons travel from cathode to anode, not the other way around.