# Physics 212, Extra Credit for Week #6: due Feb 3, 1998, at 7 PM

Build and use an isobaric chamber.

This project may be done by teams of 1-3 individuals. The goal is to design, construct, and use an isobaric chamber. If all goes well, you may be able to verify the rule for work done by an isobaric process.

You must design a container which has a movable, yet reasonably air-tight upper (or lower) surface. Perhaps you can think of some way to use an air-tight liner of some sort inside an outer container, or maybe you can imagine some way to use a water trap to keep the air stuck within a space. If you're stumped, you might ask the instructor for hints. The lid must be able to slide reasonably freely, so watch out for friction. Use lubricant if necessary -- it might help your air-tight seal. The chamber must be large enough to contain a thermometer.

Once you have a good container, with ordinary air inside, place a thermometer inside, and measure the temperature of the air. It would be best if the container were transparent, so that you could keep the thermometer inside and continue to read it throughout the experiment; but it's not necessary. You must also measure the volume of air in the container. Leave the thermometer inside your chamber.

Now, arrange your chamber so that there is a constant pressure against the lid. What is that pressure? Make sure you can measure it, or calculate it with reasonable assumptions.

Now, cool your isobaric chamber significantly. Find some way to drop the temperature of the container, and the air within, by at least 10 degrees Celsius. The larger the temperature change, the better. Perhaps you can immerse the container in cold water. As the air within cools, you should notice that the volume of the chamber decreases.

Wait either 20 minutes, or until your chamber has moved by an amount which is easily measured. Now measure the volume of the chamber. After you've done so, it's safe to open the chamber and read the temperature off the thermometer.

Calculate the change in volume for an ideal gas during an isobaric process, given the constant pressure and change in temperature for your chamber. Compare to the change in volume which you measured. Are they the same, or at least close? If not, why not?

Remember that if any air leaks out the chamber during the experiment, the volume will decrease even if the temperature were to be constant. If your chamber did leak, you'll have to find some way to fix it.

Submit a report which contains a description of your chamber, with a clear drawing and all relevant dimensions. Include the data (pressure, original volume and temperature, final volume and temperature) for your experiment, and all calculations. You may also include interesting items you discovered during the course of the procedure.