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.
From Stefan’s law we have,
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 ………