Exam 6: Some Processes Are Irreversible Thermal Physics

Classify the following hypothetical perpetual motion machines as being perpetual motion machines of the first kind $(A)$ or the second kind (B). -(e) A normal heat engine is used to drive an electric generator. Part of the power from this generator runs a refrigerator that absorbs the waste heat from the engine and pumps it back into the hot reservoir.

Suppose that when we add $20.8 \mathrm{~J}$ to 1 mol of a certain gas, its temperature is observed to increase by $1 \mathrm{~K}$ . Which of the following statements is true?

Which system has the greater entropy, a puddle of water sitting on a table next to a chaotic scattering of salt crystals or the same amount of salt dissolved in an evenly distributed way in the puddle? Be prepared to describe your reasoning.

Suppose that we place objects $A$ and $B$ into a large bucket of water and allow them to come into equilibrium with the water. If we now extract $A$ and $B$ from the water and immediately place them in contact with each other, they will necessarily be in equilibrium.

Which of the following devices are heat engines? In each case, answer T (True) if it is a heat engine, and F (False) if it is not. -(e) A rocket

Problems T7T. 3 through T7T. 7 refer to the following cyclic gas process: -The process $B \rightarrow C$ shown is

According to the text's final model (including the ocean effect), about when will the earth's average surface temperature be $288.4 \mathrm{~K}$ ?

Suppose we place a $100-\mathrm{g}$ aluminum block with an initial temperature of $100^{\circ} \mathrm{C}$ in a Styrofoam cup containing a $100 \mathrm{~g}$ sample of water at $0^{\circ} \mathrm{C}$ . (The specific heats of aluminum and water are $900 \mathrm{~J} \cdot \mathrm{kg}^{-1} \mathrm{~K}^{-1}$ and $4200 \mathrm{~J} \cdot \mathrm{kg}^{-1} \mathrm{~K}^{-1}$ , respectively.) The system's final temperature is closest to

Suppose that we double the electrical power flowing into the filament of an incandescent bulb. By what factor will the most probable photon energy $\varepsilon_{p}$ increase?

A container holds 1 million helium molecules at $300 \mathrm{~K}$ . If we double the gas's temperature to $600 \mathrm{~K}$ , by about what factor does its multiplicity increase?

Suppose that an atom has exactly two energy levels separated by an energy difference $\Delta \mathrm{E}$ . When such atoms are in contact with a reservoir at a temperature $T_{1}$ , the ratio of the number of atoms in the higher level to the number in the lower level is $\frac{1}{4}$ . If we increase the temperature to $T_{2}$ , the numerical value of this ratio

A hot object is placed in contact with a cold object. We observe that heat flows spontaneously from the hot object to the cold object, but not in the other direction. According to the argument in this chapter, this is so because

One can convert work to heat (the reverse of what a heat engine does) with perfect efficiency.

Suppose that we place an aluminum cylinder, a wooden block, and a Styrofoam cup on a table and leave them there for several hours. We then come back into the room and feel each object. -(b) Which (if any) actually is coolest?

Problems T7T. 3 through T7T. 7 refer to the following cyclic gas process: -When an object slides down a frictionless incline, The interaction does not change the object's momentum

The Carnot engine is important because

A maximally efficient Carnot engine would produce zero power.

Suppose that the temperature $T$ is about $T_{E} / 9$ for a certain Einstein solid. The probability that an oscillator in that solid will have one unit of energy is closest to (Hint: See equation $T 4.32$ for how to calculate $Z$ .) Equation T4.32: $1+x+x^{2}+\ldots=\frac{1}{1-x}$

All irreversible processes involve -(b) transfers to an object's thermal energy,

In each of the processes described below, energy flows across the boundary of the object that serves as the subject of each sentence. Is this energy flow heat (A), work (B), or some other kind of energy transfer (E)? -(e) Your pizza gets warm in the microwave.