incandescent light bulb

Blackbody Radiation


I know its a bit theoretical and less fun but I am posting this experiment for people who are really interested in physics and do not have means of getting this kind of experimental setup. Although this is a must Do-it-yourself experiment but that’s not possible, at least not in a country like India. Nevertheless, I am providing you with my raw data and the analyzed one so you can get a feel of the experiment.  (You can download the data files provided at the end of this post. Its a .rar file so you’ll first have to extract it using winrar or any other software.)

In this experiment we will investigate the radiation emitted by an incandescent light bulb. This is achieved by using a prism spectrophotometer (image below) that measures relative light intensity as a function of angle.


A Broad Spectrum Light Sensor is used with a prism so the entire spectrum from approximately 400 nm to 2500 nm can be scanned. Wavelengths corresponding to its particular angle is calculated using the equations for a prism spectrophotometer. The relative light intensity can then be plotted as a function of wavelength as the spectrum is scanned, resulting in the characteristic blackbody curve. The goal of this experiment is to determine  accurate experimental values of the Wien’s constant and of the Stefan-Boltzmann constant. The experiment is repeated for different temperature of the incandescent light bulb. Temperature of the light bulb can be changed by changing its intensity. The temperature of the filament of the bulb can be estimated indirectly by determining the resistance of the bulb from the measured voltage and current.

Click here to download data and the official guide to this experiment.