Final answer:
To adjust for an increased SID from 40 inches to 44 inches and a change in mA from 300 to 500, the new exposure time is approximately 22 ms, calculated using the inverse square law and mAs reciprocity.
Step-by-step explanation:
The student is asking about a radiographic procedure and the adjustment of exposure time to maintain radiographic density when Source-to-Image Distance (SID) is increased, and when there's a change in milliampere settings. To calculate the new exposure time when increasing SID from 40 inches to 44 inches and changing from 300 mA to 500 mA, we use the inverse square law and milliampere-seconds (mAs) reciprocity. The initial mAs (milliampere-seconds) product was 300 mA × 0.03 s = 9 mAs. The inverse square law states that the intensity of radiation is inversely proportional to the square of the distance from the source, so when the distance is increased, the mAs must be increased accordingly to maintain density. Newly required mAs using the inverse square law formula (new mAs = old mAs × (new SID² / old SID²) is 9 mAs × (44/40)² = 10.89 mAs. Then, to find the new exposure time with the increased mA, you take the new mAs divided by the new mA setting: 10.89 mAs / 500 mA = 0.02178 s or approximately 22 ms.