Operating Temperature and Heat Capacity of a Light Bulb Filament: An Experimental Problem used in the German Physics Olympiad

We present an experimental problem used in the German national competition for the In-ternational Physics Olympiad, which, due to its emphasis on accurate data acquisition and rather unusual ways of evaluating the data, seems very suitable for testing the experimental abilities and creativity of the students. The first part of the problem deals with the resistance of a light bulb filament as a function of temperature. The determination of the filament’s temperature utilizes features of its black body radiation curve and the wavelength-dependent sensitivity of a photo diode. The analysis with the given instruments requires clever application of a logarithmic plot. In the second task the heat capacity of the light bulb filament is investigated. This can be done by periodic heating and cooling of the filament. The process is driven by an appropri-ate voltage signal from a function generator and monitored using an oscilloscope. This task can also be used as a single problem, when the result of the first part is given.