A laboratory experiment on the application of Stefan’s law to tungsten filament electric lamps

Abstract

Commercially available electric lamps are used in a laboratory experiment for the verification of Stefan’s law. Assuming that the emissivity of tungsten filament remains constant and that all the filament power goes out as radiation, Stefan’s T4 law can be verified from a log-log plot of radiated power P against temperature T of the filament. It is found that correction to filament power due to convection loss is necessary for the gas-filled lamps and not for vacuum lamps. The experimental value of the slope of the graph of log P vs log T for all these lamps is found to be 5, which shows that the emissivity of the filament surface is proportional to the temperature of the filament. A simplified laboratory experiment avoiding temperature calculations and convection loss corrections is described in this study.