Kilovolt peak (kVp) primarily controls which aspect of X-ray production?

• A. The number of electrons emitted per second.
• B. The shielding thickness.
• C. The speed or energy of the electrons.
• D. The exposure time.

Answer: (C)

Kilovolt peak sets the accelerating voltage across the X-ray tube, which determines how fast the electrons are propelled from the cathode toward the anode. The faster these electrons move, the more energy they have when they strike the target, and that energy translates into the energy of the emitted X-ray photons. In other words, kVp largely controls the speed and energy of the electrons, and thus the maximum photon energy and the overall energy spectrum of the X-rays.

The other factors respond to different controls: the number of electrons produced per second is tied to the tube current (mA), exposure time affects how long you’re taking the image, and shielding thickness relates to dose and beam energy but is not what kVp directly sets. Therefore, the aspect most governed by kVp is the speed or energy of the electrons.