Workout: Heat capacity

Read

Read the web page Heat capacity.

Launch

To give you some sense for how this works, go to the the PhET simulation, "Energy Forms and Changes".

Set up

Make sure you're on the Intro tab. Turn on the "Energy Symbols" box at the upper right. Now grab each thermometer by its little arrow and play it in one of the materials. Align the thermometers to that the top of the red temperature marker is at the top of each material. (That makes changes in their temperature easier to see.) Your screen should look like this:

Answer these questions

1. All three objects are supposed to have the same volume. Since both bricks and iron sink in water, we can assume the water has the least mass of the three, the brick next, and the iron is the heaviest. Yet although all three objects have the same temperature, they have different amounts of thermal energy: the brick the fewest units, iron the next, and water the most. Why is this the case?
2. If you explained your answer to the first question in terms of "heat capacity", explain the result in terms of "the equipartition theorem" and vice versa.
3. Now put the brick and the iron onto the heat exchangers. Your screen should look like this.

Count the number of ticks on the thermometers. This represents room temperature. Remove the thermometers and count the number of energy symbols in each.

What is the ratio of the number of energy symbols in the block to the number of ticks on the thermometer? This is "temperature per energy" (related to the heat capacity).

Now remove the thermometer (so you can count the number of "E"s more easily) and add heat to each block by pulling and holding the arrow on the heat/cold generator up until a number of "E"s are added. You're probably better off by doing one at a time since the "E"s tend to leave.) Restore the thermometer and see how many ticks the temperature went up. Is the ratio of change in energy symbols to temperature change the same for the two blocks? Or is it the same as the energy/temperature ratio you found when they are at room temperature? Why do you think this is?

4. Why do the energy symbols drift off the blocks after you have heated them? To test your hypothesis, cool the blocks as much as you can and then wait. Now what happens?

Joe Redish, Fall 2016