Stefan-Boltzmann Law - If add up the contributions from all parts of the E-M spectrum, obtain the total energy emitted by a blackbody over all wavelengths.
- That total energy emitted per second per square meter by a blackbody at temperature T is proportional to the 4th power of its absolute temperature.
- This is known as the Stefan-Boltzmann law,
- E = T4 where E stands for the total energy and is a constant number.
Problem - Stefan-Boltzmann Law ET = T4 - The average surface temperature of the Sun is about 5800 K. If the Sun were twice as hot, 2 T = 2 x 5800 K = 11,600 K, how much more energy would it radiate than it does now?
- The energy radiated by the Sun would be 24 or 16 times more than now.
- E2T = (2T)4
- = (2)4 T4
- = (2)4 ( T4 )
- = 16 ( T4 )
- = 16 ET
Why Do We Need Space Telescopes? - Only a small fraction of the radiation produced by astronomical objects actually reaches our eyes because atoms and molecules in the Earth's atmosphere absorb certain wavelengths and transmit others.
- Opacity is proportional to the amount of radiation that is absorbed by the atmosphere.
- Half-Absorption Altitude (km)
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