Warm-Up Exercise 11

Due 12:15 pm, Fri 21 Sep 2012

Physics 123, Fall 2012

Reading assignment: 22.2-22.4

Why would you want to use a heat pump (instead of an electric heater) to heat your house when 100% of the energy in an electric heater can be converted directly to heat? Isn't that more efficient? Explain.

In the third paragraph of Section 22.3 (8th edition), there's a caveat that to be reversible, the gas must be able to return to its original state *without changing the surroundings*. Give an example of a process that would be considered reversible if not for that qualifier.

The Carnot engine is completely impractical---because it has to operate reversibly, it would take it an infinite time to complete a cycle. (Even operating *almost* reversibly, it will take a long time to complete a cycle---it would still be impractical.) Why then do we bother? What is important about this engine?

Why doesn't the Carnot engine have perfect efficiency?