PHYSICS

1. 1. [2 pts] Suppose a gas was injected into the atmosphere that strongly absorbed electromagnetic radiation with photon energies between 2 and 5 eV. How would this effect the amount of radiation getting to the surface of the Earth.
2. Most electrical generation depends on the production of steam, which is then used to turn a turbine to make electricity. Steam is heated to a very high temperature – about 1000 F (810 K). After going through the turbine the steam is cooled to about
360 F (455 K). The maximum efficiency from the 2nd Law is 1-TCold/Thot, which is then 1-455/810 = .44, or 44%. Actual generators have close to 40% efficiency, so they are near the theoretical maximum.
(a) (2 pts) There is a considerable effort to develop steam generation systems that can use steam at 1200 F (920 K). Explain why this is desirable.
(b) (2 pts) Using electricity to heat a house or run a car is often touted as being 100% efficient. If the electricity is generated using a steam generator, explain why this claim is misleading.
3. (a) (2 pts) Many years ago most windows consisted of a single pane of glass, with an R value of about 1. Most double pane windows have an R value of about 3. The best windows now consist of 3 panes of glass with argon gas instead of air between the outer and middle pane. The R value is about
4. Discuss why modern windows have a much
higher R value than a single pane. (Hint on argon – look up thermal conductivity of air
and argon on the web).
(b) (2 pts) Good windows are also coated to be very reflective in the infrared. Why does this help keep a home warmer in the wintertime?
(c) (4 pts) The R value of a typical insulated wall in a house is about
5. A typical house has about a ratio of wall to window of about 5 to 1 (that is the area of the wall is 5 times
that of the windows). Recall that conductive heat loss is proportional to the area divided by R. Discuss the heat loss via conduction for the wall compared to the windows for single and double pane windows. Be as quantitative as you can. Are single windows an important source of heat loss? Are double pane windows?

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