If the SID is doubled while maintaining mAs, receptor exposure will:

If the SID is doubled while maintaining mAs, receptor exposure will:

• A. Double
• B. Halve
• C. Quarter
• D. Remain the same

Answer: (C)

Receptor exposure follows the inverse square law: as the distance from the source to the receptor increases, the beam intensity at the receptor drops with the square of that distance. Doubling the SID makes the distance 2d, so the beam intensity at the receptor becomes 1/4 of what it was. With mAs held constant, the number of photons reaching the receptor per unit area decreases to one quarter, yielding quarter exposure. If you needed the same receptor exposure after changing SID, you would have to increase mAs accordingly (in this case, quadruple it).

Receptor exposure follows the inverse square law: as the distance from the source to the receptor increases, the beam intensity at the receptor drops with the square of that distance. Doubling the SID makes the distance 2d, so the beam intensity at the receptor becomes 1/4 of what it was. With mAs held constant, the number of photons reaching the receptor per unit area decreases to one quarter, yielding quarter exposure. If you needed the same receptor exposure after changing SID, you would have to increase mAs accordingly (in this case, quadruple it).