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.



A very basic experiment with Semiconductor Diodes


Diode is a two terminal electronics component which has low resistance to current in one direction but very high resistance in opposite direction. Today the most common type of diode is the one which has crystalline piece of semiconductor with a P-N junction connected to two terminals. Diodes do not follow ohm’s law. So its important to study their Current-Voltage characteristics (I-V curves). In this experiment we do exactly that. From these curves we find some important quantities like ideality factor and knee voltage. Ideality factor, also known as the quality factor  accounts for carrier recombination as the charge carriers cross the depletion region. The ideality factor ‘n’ typically varies from 1 to 2 (though can in some cases be higher), depending on the fabrication proce ss and semiconductor material and in many cases is assumed to be approximately equal to 1


Knee voltage is the voltage at which current through the diode is 1mA. It is a measure of how much energy is needed to push electrons through the diode. Temperature dependence of knee voltage is determined by placing the diode in thermal contact with hot water and allowing it to cool down. Knee voltage at different temperatures is determined and plotted in a graph (refer the pdf). From this graph we find out that knee voltage decreases with increasing temperature.  The equations used are written below and all data has been compiled in a pdf.