Exam 6: Some Processes Are Irreversible Thermal Physics

In a given macropartition, the total entropy of a system comprised of two or more parts is always equal to the sum of the entropies of those parts.

In a maximally efficient heat engine, the amount of entropy that the hot reservoir loses as heat flows out of it is exactly balanced by the entropy that the cold reservoir gains as the waste heat flows into it.

At a sufficiently high temperature, an oscillator in an Einstein solid is more likely to have one unit of energy than no energy at all.

We bring a hot object into contact with a cold object. The hot object's entropy decreases by $1.5 \mathrm{~J} / \mathrm{K}$ as it comes into equilibrium with the cold object. By how much does the cold object's entropy increase?

Suppose that an atom has two energy levels separated by an energy difference $\Delta E$ . When such atoms are in thermal contact with a reservoir at temperature $T$ , there is roughly 1 atom in the higher state for every 4 in the lower state. What is the approximate ratio of $\Delta E$ to $k_{B} T$ ?

Which of the following energy storage modes for a gas molecule "switch on" fully at -(a) the lowest temperature?

The ideal gas model assumes that molecules have infinitesimal size. Consider one molecule bouncing around in the container. As the molecule's size increases relative to the size of the container, how will the average pressure $P$ that it exerts change, other things being held constant?

According to the argument in the text, the Moon's average surface temperature (since it has no atmosphere and is the same distance from the sun as the earth) should also be $255 \mathrm{~K}$ , or it would be if all points on its surface had the same temperature (and the Moon has the same average reflectance as the earth). But the Moon rotates very slowly relative to the sun (once a month) and has no atmosphere or ocean to redistribute energy differences. How do you think that these facts might affect the Moon's average temperature? (Hint: Suppose that half the moon was $100 \mathrm{~K}$ hotter and the other was $100 \mathrm{~K}$ colder than the average. Would it still radiate as much energy as it would if its surface area were all at the same temperature?)

During an adiabatic compression, does a gas's temperature increase, decrease, or remain the same?

If an object has a multiplicity $\Omega$ that decreases as its thermal energy $U$ increases, its temperature would

You can keep your kitchen cool for hours by leaving the freezer door open.