This is the setup and calculations performed for the Fire Syringe experiment that was conducted on Wednesday. The experiment itself was a demonstration of an adiabatic thermodynamic process. In an adiabatic process, no heat is transferred into or out of the system. We were asked to calculate the final temperature of the gas after the plunger was pushed down very rapidly, and this calculation was made using the formula at the upper right hand corner of the picture. We first had to calculate the initial and final volumes of the cylinder using a ruler and a micrometer. The radius of the cylinder was determined by measuring the diameter of an o-ring which was attached to the plunger with a micrometer. The other measurements were made using a ruler, with the most uncertainty coming from the measurement of the final volume. All of the measurements and the calculated final temperature can be seen in the picture above. This final temperature is enough to ignite paper, and so it was determined that if a small piece of cotton was placed at the bottom of the syringe, it would ignite with a rapid decrease in volume of the trapped air. We carried out the experiment and saw that our hypothesis was correct.
This is an actual video of the experiment. I seem to have trouble uploading videos to this blog, so if you are unable to view it you can find it on a blog belonging to either Andrew or Dennis.
This is a screenshot of the first of six exercises we completed during class on Wednesday. We were asked which of the three graphs correctly displayed the relationship between volume and temperature in an isobaric thermodynamic process in which the pressure and the number of atoms remained constant. The correct graph is the topmost one in which the volume of a gas increases with increasing temperature. This shows that volume and temperature are directly proportional.
In the second exercise, we were asked to identify the graph that correctly displays the relationship between pressure and temperature in an isochoric process in which the number of atoms and the volume of a gas remain constant. The correct answer is the graph that is displayed at the upper left hand corner of the picture. Much like the previous graph, this shows a linear, directly proportional relationship in which the pressure of the gas increases with increasing temperature.
As you can see from the calculation, the quotient of the initial volume of gas and its initial temperature is equal to the quotient of its final volume and final temperature. The initial volume of gas was 41.6*10^-3 m^3 at 500 K. When the temperature was decreased to 301.8 K, the volume decreased to 25.1*10^-3 m^3. This answer makes sense because of the direct relationship between volume and temperature in an isobaric process.
In the fifth exercise, we were asked to calculate the final pressure of a gas after it has experienced an increase in temperature during an isochoric process. The initial pressure of the gas was 42*10^3 Pa at a temperature of 100 K, and its pressure increased to 126*10^3 Pa after the temperature was increased to 300 K. This is another example of a direct relationship between two state variables in a thermodynamic process.
In the last exercise we completed on Wednesday, we were asked to determine the final pressure of gas as the volume of that gas decreased in an isothermal process. One can see from the whiteboard that the product of the initial pressure and volume equals the product of the final pressure and final volume. In the first part, the volume decreased from 40*10^-3 m^3 to 20*10^-3 m^3 resulting in an increase of pressure from 62 kPa to 125 kPa. The same process was used to calculate the final pressure of the gas as its volume decreased even further to 10*10^-3 m^3.
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