According to the inverse square law, doubling the SID results in receptor exposure changes of approximately:

According to the inverse square law, doubling the SID results in receptor exposure changes of approximately:

• A. Doubles
• B. Halves
• C. Quadruples
• D. Quarter

Answer: (D)

The main concept is the inverse square law: receptor exposure is inversely proportional to the square of the distance from the X-ray source. If you double the SID, the distance is 2, so the exposure scales by 2^2, which is 4. That means the exposure at the receptor becomes one quarter of the original value (25%). If you needed the same exposure with a doubled SID, you’d have to increase the technique factor fourfold (for example, quadruple the mAs). The other options would imply linear or greater changes, which the square relationship does not support.

The main concept is the inverse square law: receptor exposure is inversely proportional to the square of the distance from the X-ray source. If you double the SID, the distance is 2, so the exposure scales by 2^2, which is 4. That means the exposure at the receptor becomes one quarter of the original value (25%). If you needed the same exposure with a doubled SID, you’d have to increase the technique factor fourfold (for example, quadruple the mAs). The other options would imply linear or greater changes, which the square relationship does not support.