Chapter 8
Exercises
1. Twice as hot would be 293º C.
2. Twice as cold, or half the temperature, would
be 131.5º C.
9. The greater air pressure at a lower altitude
would compress the bag and thus raise the temperature of the gas inside.
14. The efficiency is best when the temperature difference between input and output is greatest. One way to increase this difference, and hence the efficiency, is to use as high a temperature steam as possible.
15. Efficiency is higher when the temperature between
the heat source (combustion chamber in the engine) and the sink (air surrounding
the exhaust) is greatest. Strictly speaking then, efficiency is greatest
when the outside temperature is coldest.
17. Decrease the temperature of the sink while
holding the source constant is the most efficient way to increase efficiency.
Increasing the source only alters both the numerator and denomenator of
the efficiency formula.
18. Ideal efficiency = 0.88 or 88%.
20. No change in temperature will occur. The refrigorator
moves heat from the inside of the refrigerator to the outside of the refrigerator,
i.e. the kitchen. Leaving the door open will move heat from the kitchen
to the kitchen.
23. The temperature of the surrounding air decreases.
28. If the building is heated electrically, leaving the lights on is not wasteful. The electricity provided to the bulbs is efficiently turned into heat., thus it would be wasteful if the building is being cooled.