Phy101 GDB IDEA solution June 2012

Phy101 GDB IDEA solution June 2012

"Is there entropy changes associated with the transmission of energy from the sun to the
earth? Are the earth and sun in thermal equilibrium?
Does radiation differ from other modes of heat transfer with respect to the entropy
changes?" Explain your answer with reasoning.
Solution: 1
In the given condition the Sun becomes more entropic while the Earth's biosphere
becomes less entropic. Here the main reason is Earth can become less entropic, which
you may have heard is impossible, is because the Earth is NOT a closed system. It has an
input, the Sun. However, on the other hand the decrease in Earth's entropy is less than the
increase in the Sun's entropy, so overall entropy increases as it always must. So this is
further explanation of my reason
 Solution: 2
Is there entropy changes associated with the transmission of energy from the sun to the
earth?
YES  Entropy = S = integral dQ/T
As Earth has a lower temp, the entropy increase from insolation is lower than the entropy
decrease of the Sun, demonstrating a net increase in entropy.
Another similar note: look at DeltaS on Earth, as sunlight comes and reradiation at night
cools the Earth, and see that that reradiation gives a higher entropy than insolation, so
there is room for us on Earth to create entropy.