- The solar constant is defined as the total radiant power of the Sun, per square metre, received at the Earth's orbit (outside of the Earth's atmosphere).
a) You must treat the illuminated face of the Earth as if it were a disk, not a hemisphere, when calculating the total area of sunlight falling on the Earth's surface. Can you explain why?
b) Using the radius of the Earth, and the solar constant, calculate the total radiant power incident on the Earth's sunlight surface.
- In order for the Earth to remain (on average) in thermodynamic equilibrium, how much electromagnetic power must the Earth radiate into space?
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Given that, on average, the Earth radiates electromagnetic energy uniformly from its entire surface, what is the global average power (W·m-2) emitted per square metre of the
Earth's surface?
(Surface area of a sphere 4(3.14)r2)
- a) Using the Stefan-Boltzmann law, Epower = 5.79x10-8T4 calculate the equilibrium temperature of the Earth using your results from question (3) above.
b) Compare this to the current value of approximately 290K. Can you account for the difference?
- The Universe is bathed in weak microwave radiation which appears isotropic and constant. Its spectrum resembles that of a perfect black-body whose electromagnetic spectrum peaks at
9.66x10-4m. This is the cosmic microwave background which was predicted by George Gamow in 1948. Using Wien's Displacement Law ( ) calculate the temperature of this background radiation.
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Einstein's famous equation, (which solved the perplexing photo-emission dilemma) is given as,
E= hf Use this equation to
calculate the frequency and the wavelength of a 4.5MeV gamma ray from the alpha decay of radium 88Ra226.
- Calculate the frequency and the wavelength of a 185.7keV gamma ray from the alpha decay of radon 86Rn222.
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