Inquiring into a spectral concept in the physics classroom

We designed an inquiry activity to investigate the question ‘How transparent are transparent films and papers?’ Using an easily-replicable set up, we observed the effect of increasing the number of transparent films, thin papers and general papers between a light source and a light sensor. For each material, one sheet was added each time. The amount of light received was collected and graphed by a data logger. Our findings show that, as the number of sheets increases, the amount of light received at the receiver decreases. The general paper and thin paper stacks took 4 sheets and 10 sheets respectively to achieve negligible light transmittance. The transparent film stack did not achieve negligible light transmittance, but successive addition of sheets did lower transmittance. Evidently, transparent films are not perfectly transparent. Transparency (and opacity) is not a binary condition, but rather a continuum based on boundary conditions. The inquiry activity developed through this study, which investigates a spectrum of transparency in films and papers, may be useful for students to appreciate the spectral nature of the transparency concept across different materials.