Which symbol represents distance in the Beer's Law formula?

• A. C
• B. D
• C. a
• D. e

Answer: (B)

Beer's Law links absorbance to three factors: how much solute is present (concentration), how strongly the solute absorbs light at that wavelength (molar absorptivity), and how far the light travels through the sample (distance or path length). The distance the light travels is the path length, which determines how much of the light is absorbed as it passes through the sample. In the particular formula used here, that distance is denoted by the letter D. So D stands for the path length, the distance light covers inside the sample. For a fixed concentration and molar absorptivity, increasing D increases absorbance proportionally. The other symbols correspond to concentration and absorptivity, not distance.