In Beer's Law, if the concentration doubles and the absorptivity and path length remain constant, what happens to absorbance?

• A. Absorbance doubles
• B. Absorbance halves
• C. Absorbance remains the same
• D. Absorbance increases quadratically

Answer: (A)

Beer's Law tells us that absorbance is proportional to concentration when the molar absorptivity and path length are constant, expressed as A = ε l c. If you double the concentration while ε and l stay the same, the absorbance doubles because A scales linearly with c. More absorbing molecules along the path means more photons are taken up, so the measured absorbance increases in direct proportion to the concentration. The other options don’t fit this linear relationship: halving the concentration would halve absorbance, keeping the concentration the same wouldn’t change absorbance, and a quadratic increase would imply A ∝ c², which isn’t how Beer's Law describes the dependence.