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Stephen-Boltzmann Law
In the year 1879, a scientist named Stephen experimentally showed that "the amount of energy radiated by a surface, in the form of thermal radiation, per unit area per second is proportional to the fourth power of its absolute temperature". The same fact was theoretically established by Boltzmann in the year 1884. The statement is known as StephenBoltzmann law.
The amount of energy radiated per second per unit area at a given temperature is called the total emissive power. The total radiated energy includes the entire amount integrated over all the frequencies of electromagnetic spectrum. So according to Stephen-Boltzmann law, W = e Q T1. (6.36)
Here, T is the absolute temperature, e is known as the emissivity of the radiating surface, Q is called the Stephen-Boltzmann constant. It is a universal constant and has value of Q = 5.67 x 10-8 Watt/met2 K4)"
104. 2, pages 199, 200
"In reality, the electric current in solids is due to motion of electrons, so one may say that a unit negative charge has an electrical energy of V Joule at the negative terminal.
We have also studied in the previous chapter that when the electrons acquire drift they experience collisions with the positive ions oscillating about their mean position; and the energy acquired by the electrons is partly handed over to the ions making their oscillations more energetic. This increase in the energy of oscillations of the ions is manifested as heat, causign an incerease in the temperature of the conductor.
The heat energy released in a conductor on passage of an electric current is called the 'Joule heat' and the effect is called the 'Joule effect".
If the potential difference applied across two ends of a conductor is V; it means that when a unit charge passes through the conductor, an amount of electrical energy equal to V Joule is utilized.
If Q coulomb of charge passes through the conductor in t seconds then the electrical energy utilized in t seconds = heat energy produced during this time.
"Joule's Law: "The heat produced per unit time, on passing an electric current through a conductor at a given temperature, is directly proportional to the squre of the current."
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