Quantitative experiments in a distance lab: Studying blackbody radiation with a smartphone

In this paper we present an experiment aimed at investigating the thermal radiation law. The spectrum of a filament light bulb is acquired at different temperatures using a low-cost grating spectrometer based on a smartphone camera, while the measurement of filament temperature is obtained indirectly from the temperature dependence of the filament resistance. Two different methods for measuring the light intensity are tested: one is based on the use of the ambient light sensor of a smartphone, the other on a home-made grating spectrometer coupled with the smartphone camera. We observe a good agreement of the experimental data with the theoretical predictions of the Planck distribution in the limit of the Wien approximation restricted to the wavelength range characterizing the response of the smartphone light sensor and camera.