Verification of Stefan Boltzman’s Law

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BACKGROUND

All the bodies either absorb, transmit, or radiate the emitted radiation falling over its surface. A black surface is the one which absorbs all the radiation falling on it. Thus, it has zero value of reflectivity and transmissivity while its absorptivity is unity.¹

Stefan Boltzman’s law determines the total energy radiated by an object by using the value of its absolute temperature. This law states that objects radiate energy based on the fourth power of their absolute temperature.²

i.e. E a T⁴

or, E = seT⁴

where, E= Emissivity power of the surface (W/m²)

T= Absolute Temperature (K)

s=Stefan Boltzman Constant (W/m²K⁴)

e= Emissivity of the surface

Value of Boltzman Constant is always taken as 5.667* 10^-8 W/m²K⁴,

And, for a black body, e=1,

Thus, E=s.T⁴

The apparatus used in this experiment consists of a hemispherical shaped water heated jacket which is fitted with copper test disc in its center. The hot water is used to increase the hemisphere temperature, which is collected from the hot water tank. Thermocouples are used to measure the test disc’s temperature, and a timer is used to measure the temperature after every 5 seconds of interval.³

The main purpose of this experiment is to study the verification of Stefan Boltzman’s law.

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REQUIREMENTS

Materials: Ammeter

Voltmeter

Thermocouple

Timer

Buzzer

Electric Immersion Heater

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PROCEDURE

First of all, switch ON the heater, and close the inlet cock of the water jacket and then fill sufficient water in the heater tank. After this, boil the water and then put the thermometer to check water temperature after putting the heater ‘OFF’. Check the level of water above the top of hemisphere, and ensure if drain cock of water jacket is closed, and then open the inlet cock. Add water in the hemisphere if required. Now, note down the hemisphere temperature (up to channel 1 to 4) and the test disc temperature (channel 5). After this, start the timer and buzzer, and note down the disc temperature and insert the test disc into hole.

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CONCLUSION

The process of verification of Stefan Boltzman’s law has been discussed. The emissivity of any surface varies in a direct relationship with the fourth power of the absolute temperature of the body.

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REFERENCES

Z. L.-L. Francois Becker, “Surface temperature and emissivity at various scales: Definition, measurement and related problems,” Journal of Remote Sensing, vol. 12, no. 3-4, pp. 225-253, 1995.
P. T. L. a. A. D. Vos, “The Stefan-Boltzmann constant in n-dimensional space,” Journal of Physics A: Mathematical and General, vol. 22, no. 8, 1994.
E. E. K. I. A. Sidra Khalid, “Filament temperature of low power incandesecent lamps,” Journal of Physics, vol. 4, no. 2, pp. 1870-1905, 2010.