Determination and Verification of Stefan’s Constant


To determination and Verification of Stefan’s Constant.


The experimental set up consists of a vacuum diode with a cylindrical cathode made up of nickel. Closely fitted with the cathode sleeve is the tungsten heater filament. Temperature of the filament can be determined using the known resistance (R) – temperature (T) relationship for tungsten. Temperature coefficient of resistance for tungsten remains constant up to very high temperature and the R-T relation for tungsten is expressed in the form:

Applying Stefan’s law to the heated cylindrical cathode we can determine Stefan’s Constant from the knowledge of the surface area and the emissivity of the cathode.

Formula Used:

From Stefan’s law we have,

Experimental Results:

Determination and Verification of Stefan’s Constant

Plot a graph with log P along Y-axis and log T along X-axis.


We know That,


The measured value of Stefan’s constant (σ) is ………


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