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This lab gives students a chance to take data on the first day of class (or later, but I prefer to do it the first day of class). It provides an immediate context for thermodynamics, and also gives them a chance to experimentally measure a change in entropy. Students are required to measure the energy required to melt ice and raise the temperature of water, and measure the change in entropy by integrating the heat capacity.
Estimated Time: 50 minutes
The students will set up a Styrofoam cup with heating element and a thermometer in it. They will measure the temperature as a function of time, and thus the energy transferred from the power supply.
This lab is very simple to run, but to get it done in one period you'll need to get students working quickly to measure the ice and water and get their heating started. Once their labs are going, there is time to give a middle-of-lab lecture introducing thermodynamics and thermal measurements.
There are two things to keep in mind for this lab. One is that the ice-water cups need to be vigorously stirred, otherwise the hot water (around 4 degrees Celsius) will settle at the bottom while the cold ice floats on the top. The other is that the ice should be cubes (not crushed) and the water should be ice-cold before it is massed out, otherwise too much ice will melt immediately on being added to the water.
Once the measurements are taken, I asked the students a couple of small-whiteboard-questions, “What is heat?” and “What is entropy?”. I then lecture on what the heat capacity $C_p$ is, and how they could extract it from their data, and on how they can calculate entropy from their measurements: $\Delta S = \int \frac{dQ}{T}$.
Many students have difficulties simply measuring the water and ice correctly. Perhaps smaller containers for retrieving water would be good (around the same size as necessary). Or perhaps some basic lab procedures need to be gone over at some point in the Paradigms. Once the basic lab setup was accomplished, students seemed able to do the rest of the lab with no difficulty. -Amanda Abbott
At the end of the lab, students should know how to calculate the entropy from the change in temperature. Students should be given a few days to do the analysis, and the data that they collect should be distributed to each member of the group.