The rule or law that governs changing technique using kVp is the:

The rule or law that governs changing technique using kVp is the:

• A. Inverse square law
• B. Density maintenance law
• C. Reciprocity law
• D. 15% rule

Answer: (D)

When you change the kilovoltage to adjust technique, you want to keep the same exposure on the image receptor. The 15% rule is the guideline used for this. It states that increasing kVp by about 15% allows you to cut the mAs in roughly half to maintain the same receptor exposure, and conversely, decreasing kVp by about 15% requires doubling the mAs. This helps balance image density and contrast: higher kVp increases penetration and reduces contrast, so you offset that by adjusting mAs to keep the overall exposure similar. The other concepts relate to different relationships—distance affects intensity via the inverse square law, and reciprocity deals with exposure depending on the total mA×seconds regardless of how time and current are combined—but they don’t specifically describe how changing kVp should drive adjustments in technique to preserve exposure.

When you change the kilovoltage to adjust technique, you want to keep the same exposure on the image receptor. The 15% rule is the guideline used for this. It states that increasing kVp by about 15% allows you to cut the mAs in roughly half to maintain the same receptor exposure, and conversely, decreasing kVp by about 15% requires doubling the mAs. This helps balance image density and contrast: higher kVp increases penetration and reduces contrast, so you offset that by adjusting mAs to keep the overall exposure similar. The other concepts relate to different relationships—distance affects intensity via the inverse square law, and reciprocity deals with exposure depending on the total mA×seconds regardless of how time and current are combined—but they don’t specifically describe how changing kVp should drive adjustments in technique to preserve exposure.