Absorption spectroscopy is an analytical technique that measures the amount of light absorbed by a sample at specific wavelengths of the electromagnetic spectrum. The underlying principle is that when electromagnetic radiation passes through a substance, the molecules absorb energy at characteristic frequencies, causing transitions between different energy levels—such as electronic, vibrational, or rotational states. By quantifying the intensity of the light beam before and after passing through the sample, concentrations of absorbing species can be determined based on the Beer-Lambert law, which relates absorbance to concentration and path length. This method is widely utilized across chemistry, physics, and biology for the qualitative identification and quantitative determination of various chemical components in solutions and materials.