Lesson 22

1. We've analyzed a situation in which an ideal gas is allowed to expand isothermally (and reversibly, which just means it happens very slowly). Now let's look at a situation in which the same ideal gas is allowed to expand isentropically (and reversibly). In both cases, the gas doubles its volume.

What's the same in each of these cases, and what's different? [Hint: Consider in particular where the energy comes from to do the work needed to push the piston.]

Enter your answer here:

2. Suppose your cadet squadron room has a movable ceiling so that the volume of your room can be changed. Suppose further that your room is completely isolated from any thermal reservoirs. This means that, if you were to change the volume of your room sufficiently slowly so that the process could be considered reversible, you'd be changing the volume of your room isentropically. Suppose further that the initial temperature of your room is a sweltering 40 degrees C (313 K).

Estimate the volume change you'd need to cause in order for your room to cool off to a comfortable 20 degrees C (293 K). Will you have to raise or lower your ceiling? By about how much will you need to raise/lower it? (Don't forget to state any estimates/assumptions you make.)

Enter your answer here:

3. Consider isothermal and isentropic expansions of an ideal gas. The pressure p

Check the correct answer:
a) varies more rapidly with volume V in the isothermal case than in the isentropic case.
b) varies more rapidly with volume V in the isentropic case than in the isothermal case.
c) varies the same way with volume V in both the isothermal and isentropic cases.
d) varies with temperature T, not with volume V.

Below is a space for your thoughts, including general comments about today's assignment (what seemed impossible, what reading didn't make sense, what we should spend class time on, what was "cool", etc.):

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