Teaching light absorption and the Beer-Lambert law using everyday materials: a tomato juice experiment for introductory physics

Abstract

I describe a visually engaging experiment to demonstrate the Beer-Lambert law in introductory physics or general science courses. By using diluted tomato juice as a naturally colored absorber and a halogen lamp as a broadband light source, students can explore how light attenuation depends on concentration and wavelength. The activity connects the optical concept of exponential absorption with everyday materials, making it accessible for classrooms with limited resources. Transmission spectra obtained with a compact spectrometer reveal a strong absorption band around 500 nm, corresponding to the green-blue region absorbed by lycopene. Plotting absorbance against concentration allows students to confirm linear behavior at low concentrations and to discuss deviations at higher ones. The experiment emphasizes conceptual understanding of light-matter interaction, quantitative data analysis, and the limitations of ideal laws, providing a memorable learning experience in optics and spectroscopy.