How is an X-ray produced?

• A. Electrons at cathode collide with the anode
• B. Photons emitted by anode
• C. Electrons from anode collide with cathode
• D. High-frequency waves heat the filament

Answer: (A)

X-rays come from the collision of high-energy electrons with a heavy metal target inside the X-ray tube. Electrons are produced at the cathode by heating, then accelerated toward the anode by the applied voltage. When these electrons strike the anode, their kinetic energy is converted into X-ray photons, through processes like bremsstrahlung and characteristic radiation. This makes the description of electrons at the cathode colliding with the anode the best fit. The other ideas don’t describe the actual mechanism: photons aren’t emitted by the anode to create X-rays, electrons from the anode colliding with the cathode would reverse the process, and heating the filament with high-frequency waves doesn’t produce X-rays.