1. We can think of a "Carnot engine" as consisting of 4 basic components: a heat reservoir at higher temperature Th, a heat reservoir at lower temperature Tl, a gas system contained inside a cylinder with a movable piston that can convert thermal energy into mechanical work, and (something we sometimes don't include) an external system on which work can be done. We might think of the external system as a large, frictionless flywheel that can store mechanical energy (or give it back, if needed).
The "Carnot cycle" consists of 4 phases or sub-cycles. In a "four-stroke" internal combustion engine (as in most cars), the four cycles are called
What is the net result of one complete Carnot cycle?
Enter your answer here:
2. Suppose you have a standard refrigerator that consumes about 160 W in normal operation. Use reasonable estimates for Th and Tl to estimate an upper limit for how much heat (Ql, measured in Joules) could be extracted from the refrigerator per second.
If all of this extracted heat were to come out of an ice cube tray of water initially at room temperature, about how long would it take to cool the water down to freezing? [Hint: Take an ice cube tray to contain 12 ice cubes of about 30 grams each. The specific heat of water is 1 cal/(g deg C) or 4.186 J/(g deg C).]
Comment on the result of your calculation.
3. Heat and work
Check the correct answer: a) can be thought of as equivalent energy transfer processes.b) are path independent processes and so can be considered to be "state functions."c) can characterize system properties.d) are path dependent processes. 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.): You may change your mind as often as you wish. When you are satisfied with your responses click the SUBMIT button.
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