In an effort to keep up with everyone in their affluent neighborhood, your friends have decided they must have a new luxury build-in refrigerator. The fact that they never eat at home is simply not the point. But despite their need to be trendy, they remain committed to energy conservation and ask your advice about how to make their new toy as energy efficient as possible.
1. If they locate the new refrigerator in the central column of their enormous kitchen, the refrigerator will be completely surrounded by the kitchen and its air. What effects, if any, will the operation of this refrigerator have on the room air's thermal energy and temperature? Explain.
2. You suggest installing the new refrigerator in an outer wall of the house, so the refrigerator's doors open into the kitchen but its back has access to the outdoor air. By sliding a panel to one side or the other, your friends can choose whether to open the refrigerator's compressor and condenser to outdoor air or to indoor air. During which season of the year would having those components open to the outdoor air make the refrigerator most energy efficient? Explain.
3. Insulating the refrigerator's doors is always a good idea because it keeps the food in the refrigerator from exchanging heat with the room air. But insulating the refrigerator's compressor and condenser is always a bad idea. Why?
4. The refrigerator has been installed as you suggested but is presently operating so that its compressor and condenser are exposed to room air from the kitchen. A six-pack of root beer has been sitting for hours on the counter next to the refrigerator. Your friend opens the refrigerator door, puts the six-pack on the ice-cold shelf, and closes the door. The refrigerator hums quietly as it begins to do its job of cooling the root beer. As the refrigerator cools the root beer, how is entropy changing, if at all, in (a) the root beer, (b) the refrigerator's food compartment (excluding the root beer itself), (c) the room air, and (d) in total for the entire house? (Note: assume that the food compartment's temperature remains constant while the root beer is being chilled. You don’t have to explain your answers to these 4 questions.)
The
only thing perpetual about perpetual motion machines is people's interest in
trying to invent them despite any history of success. Because of your strong
background in physics and thermodynamics, you decide to sell short when the new
high-tech startup company "perpetualmotion.com" conducts its initial
public stock offering. Naturally, you make a fortune and wind up in perpetual
motionlessness on a beach somewhere in the Caribbean.
5. One of the products that perpetualmotion.com announced at its press conference, held just before it started selling shares, was a device that the company claimed could produce electric power endlessly without having to come in contact with any external objects or materials. According to the press release, all you had to do was connect wires to its two terminals and it would send electric power out through those wires forever. At the conference, they used the device to light a light bulb for an hour or two. This device looked exactly like a suitcase full of D batteries. In fact, when the Justice Department eventually raided the company's headquarters, is was discovered that the device actually was a suitcase full of D batteries. However, you knew immediately that the device was fraudulent because it violated one of the laws of thermodynamics. Which law did it violate and why?
6. A second perpetualmotion.com device was said to be able to produce electricity endlessly so long as you immersed it completely in a bath of hot water at a uniform temperature. The device supposedly used heat from the hot water to generate electricity. Oddly enough, this device looked exactly like a waterproof suitcase containing... you guessed it: D batteries. To make a long story short, you knew it was a fraud because it violated another law of thermodynamics. Which law was the problem this time and why?
7. The company's most sophisticated unit for generating electricity consisted of a heat pump and a heat engine. An electrically operated air conditioner pumped heat from one container to another, creating a hot container and a cold container. A heat engine then used the hot and cold containers to generate electricity. While we haven't yet studied heat engines in class, you are aware that heat will flow naturally from the hot container to the cold container and should not be surprised to learn that some of that heat can be diverted before it reaches the cold object and converted into useful work instead. In the present case, the work takes the form of electric power that is then split in half. Half of this power is used to operate the air conditioner mentioned earlier and the other half is available as the output of this wonderful power source. As usual, the device looked like luggage, but this time it was a garment bag with a matching carry on. Despite the complexity of this machine, you were sure it was fraudulent, too. Why couldn’t the output of the heat engine be enough to power the heat pump and still have enough power to do other things as well? (Assume that the device operated in an environment at a single uniform temperature. I'm not looking for a detailed analysis of the parts here, just a statement about its overall behavior and the impossibility that the machine can do what it claims to do.)
8. In a last ditch
effort to keep the company afloat after the feds began to go after it, the
company started producing power the old fashion way: by burning fuel. They used
the only fuel they could find: tens and twenties. The crisp green bills burned nicely
but didn't provide enough power to keep the company out of bankruptcy. In an
effort to recover their investments, the creditors carefully collected all the
burned bills, the smoke that was produced, and the energy that was generated.
But try as they might, they could not get this collection of stuff to turn back
into unburned bills and fresh air. The laws of motion didn’t stop this
unburning process, so what is? Why don't the bills unburn?