The number of electrons that flow from the cathode to the anode in the tube is controlled by:

The number of electrons that flow from the cathode to the anode in the tube is controlled by:

• A. kVp
• B. SID
• C. mA
• D. OID

Answer: (C)

The number of electrons flowing from the cathode to the anode is determined by the filament current. Heating the filament with a higher mA increases thermionic emission, so more electrons are available to be accelerated. The kilovoltage mainly sets how energetic those electrons are, not how many are emitted. Therefore the tube current, and thus the electron flow, is controlled by the mA setting (with the total exposure also depending on exposure time, i.e., mAs). The other factors—kVp, SID, and OID—affect the energy and the beam’s intensity at the image receptor through different mechanisms, but they do not set the emission rate from the filament.

The number of electrons flowing from the cathode to the anode is determined by the filament current. Heating the filament with a higher mA increases thermionic emission, so more electrons are available to be accelerated. The kilovoltage mainly sets how energetic those electrons are, not how many are emitted. Therefore the tube current, and thus the electron flow, is controlled by the mA setting (with the total exposure also depending on exposure time, i.e., mAs). The other factors—kVp, SID, and OID—affect the energy and the beam’s intensity at the image receptor through different mechanisms, but they do not set the emission rate from the filament.