Reciprocity law states that the relationship between exposure and optical density (OD) should remain constant regardless of the exposure rate. In this experiment two different detectors were used to prove the reciprocity law using an exposure meter detector and a screen-film system. Four different valuesof kVps were used in this experiment which were 40 kVp, 50 kVp, 60 kVp, and 70 kVp. Different values of mAs were used from 1 mAs up to 50 mAs. Other factors used in this experiment were maintained constant such as the distance from focal spot to detector 100 cm and collimator opening 15 cm x 10 cm to make sure all contributions from the surroundings were approximately the same. In this experiment, acceptability range of the reciprocity law used for the screen-film OD was ±5% and acceptability range of the absorbed dose using the exposure meter was ±10%. From the result, it shows that at low kilovoltage which was 40 kV the OD and absorbed dose values disobeyed the reciprocity law, but at high kilovoltage, the OD and linearity value obeyed the reciprocity law
