Stefan – Boltzmann law , statement that the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature. The law applies only to blackbodies, theoretical surfaces that absorb all incident heat radiation.
In thermochemistry the Stefan – Boltzmann constant is often expressed in cal⋅cm−2⋅day−1⋅K−4: σ ≈ 11.7×10−8 cal cm−2⋅day−1⋅K−4. In US customary units the Stefan – Boltzmann constant is: σ ≈ 1.714×10−9 BTU⋅hr−1⋅ft−2⋅°R−4.
The Stefan –Boltzmann law , also known as Stefan’s law , states that the total energy radiated per unit surface area of a black body in unit time (known variously as the black-body irradiance, energy flux density, radiant flux, or the emissive power), j*, is directly proportional to the fourth power of the black body’s
Every one second, P joules of energy are radiated from the surface of the sun and this energy passes through the surface of a sphere of radius D centered at the sun . The energy passing through a unit area per second = P/4πD2 = 1.4 * 103 Wm–2. Therefore P = 4π(1.5 * 1011)2 * (1.4 * 103) W = 3.96 * 1026 W.
The Stefan -Boltzmann Law explains how much power the Sun gives off given its temperature (or allows scientists to figure out how hot the sun is based on how much power strikes the Earth in a square metre). The law also predicts how much heat the Earth radiates into space.
Thus Newton’s Law of Cooling is derived (or deduced) from Stefan’s Law. Limitations of Newton’s Law of Cooling: This law is applicable when the excess temperature of a body over the surroundings is very small (about 40oC) When the body is cooling the temperature of the surrounding is assumed to be constant.
|Click symbol for equation|
|Stefan – Boltzmann constant|
|Numerical value||5.670 374 419 x 10–8 W m–2 K–4|
|Relative standard uncertainty||(exact)|
B(T)=∫∞02hc2(kTxh)3(1ex-1)(kTh) x=2k4T4c2h3∫∞0x3dxex-1. 11-z. ∫∞0x3dxex-1=∫∞0x3(∞∑m=1e-mx) x.
The maximum rate at which its temperature will fall is (take e=1, Stefan’s constant σ=5. 8×10−8Wm2K−4 and specific heat of the metal = 90 cal/kg/deg J = 4.2 J/cal)
The energy associated with a single photon is given by E = h ν , where E is the energy (SI units of J), h is Planck’s constant (h = 6.626 x 10–34 J s), and ν is the frequency of the radiation (SI units of s–1 or Hertz, Hz) (see figure below).
radiation : energy transferred by electromagnetic waves directly as a result of a temperature difference. Stefan-Boltzmann law of radiation : Qt=σeAT4 Q t = σ e A T 4 , where σ is the Stefan-Boltzmann constant, A is the surface area of the object, T is the absolute temperature, and e is the emissivity.
Blackbody , in physics, a surface that absorbs all radiant energy falling on it. The term arises because incident visible light will be absorbed rather than reflected, and therefore the surface will appear black . The concept of such a perfect absorber of energy is extremely useful in the study of radiation phenomena.
The surface of the Sun produces sound waves because the surface is convecting and this produces pressure waves that travel into the inner corona. But yes, the surface does produce sound waves, but they have very low wavelengths measures in hundreds of miles!
At Earth’s average distance from the Sun (about 150 million kilometers), the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter, according to measurements made by the most recent NASA satellite missions.
Sources indicate an “Average over the entire earth” of “164 Watts per square meter over a 24 hour day”. The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D3 synthesis and a mutagen.