What does controlling milliamperes (mA) affect in an X-ray tube?

• A. The energy (speed) of the electrons.
• B. The number of electrons fired from the cathode.
• C. The energy of the photons.
• D. The duration of exposure.

Answer: (B)

The main idea is that milliamperes set the tube current, which controls how many electrons are emitted from the cathode each second. More milliamperes means more electrons flow toward the anode, increasing the number of interactions that produce X-ray photons. The speed of those electrons, and thus the energy of the photons, is determined by the accelerating voltage (kVp), not by the filament current. The duration of exposure is a separate setting that governs how long the tube is on; the total exposure is roughly the product of current and time (mA × time). So increasing mA changes how many electrons—and therefore how many photons—are produced, not their energy or the exposure time.