Which principle states that the product of current and exposure time yields the same receptor exposure if the mAs is the same?

Which principle states that the product of current and exposure time yields the same receptor exposure if the mAs is the same?

• A. Reciprocity law
• B. 15% rule
• C. Inverse square law
• D. Ohm's law

Answer: (A)

Reciprocity in radiography: the total amount of x-ray exposure reaching the receptor depends on the product of the tube current and the exposure time, mA × time (mAs). If you change mA and time but keep their product the same, you deliver essentially the same number of x-ray photons to the image receptor, so the receptor exposure stays the same—as long as other factors like kVp (beam quality), distance, filtration, and motion remain constant. You can substitute a high mA with a shorter exposure or a lower mA with a longer one to achieve the same mAs without changing the overall exposure, within typical clinical ranges. The rule has limits, though; extremely short or long exposures can introduce issues like quantum mottle or tube limits, which can affect image quality. The other concepts mentioned describe different relationships: the 15% rule involves adjusting mAs when changing kVp to maintain exposure, the inverse square law deals with how distance affects exposure, and Ohm's law applies to electrical circuits, not directly to receptor exposure.

Reciprocity in radiography: the total amount of x-ray exposure reaching the receptor depends on the product of the tube current and the exposure time, mA × time (mAs). If you change mA and time but keep their product the same, you deliver essentially the same number of x-ray photons to the image receptor, so the receptor exposure stays the same—as long as other factors like kVp (beam quality), distance, filtration, and motion remain constant. You can substitute a high mA with a shorter exposure or a lower mA with a longer one to achieve the same mAs without changing the overall exposure, within typical clinical ranges. The rule has limits, though; extremely short or long exposures can introduce issues like quantum mottle or tube limits, which can affect image quality. The other concepts mentioned describe different relationships: the 15% rule involves adjusting mAs when changing kVp to maintain exposure, the inverse square law deals with how distance affects exposure, and Ohm's law applies to electrical circuits, not directly to receptor exposure.