Stevens High School AP Physics II Laboratory Manual
The purpose of this lab is for you to measure pressure as a function of temperature for a fixed
volume of air. Furthermore, you are to determine the value of absolute zero (0 K) based on extrapolation of
your results.
The ideal gas law states that, for a fixed volume and amount of an ideal gas, the pressure and
temperature should be directly proportional:
𝑃𝑉 = 𝑛𝑅𝑇
(1)
𝑛𝑅
𝑃 = ( )𝑇
𝑉
(2)
If we plot pressure on the vertical axis and temperature on the horizontal axis, we would expect a linear line
passing through the origin (if T is measured in Kelvin). Why? This is the definition of 0 K. At 0 K, molecules no
longer translate (i.e., they no longer move around in space). Thus, they cannot collide with walls and the
pressure is zero. If we instead plot the Celsius temperature on the horizontal axis, then the zero pressure point
should, ideally, correspond with -273.15 oC. You will attempt to measure absolute zero in this lab which is pretty
freaking awesome if you ask me.
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PVC pressure vessel with gauge
Digital thermometer
Ice bath
Dry ice cooler
Sink
1. Start with your room-temperature pressure vessel, and record the pressure as precisely as possible. You
may record in either psi or bar. Read the gauge markings carefully! Try not to handle it as this will
change its temperature.
Note: It should read approximately 10 psi (or 0.69 bar). See Dr. Smith if this is not the case.
2. Record the room temperature (in oC).
3. Next, place your pressure vessel into a sink filled with HOT water so that the top and the gauge are kept
dry!
4. Hold and swirl the vessel and allow approximately 5 minutes for the temperature and pressure to
equilibrate to the new environment, and then record them.
5. Next, place the vessel in the ice bath for several minutes, again allowing it to equilibrate before making
pressure and temperature measurements.
6. Finally, go to the dry ice cooler which should contain a pressure vessel ready to be read. USE TONGS.
Note: Your public school thermometer can’t read the -80oC temperature of the dry ice. Assume instead
that the vessel temperature is -65oC. Trust me. I’m a doctor. If you don’t trust me, please go buy
thermometers that read low enough and donate them. Please.
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Stevens High School AP Physics II Laboratory Manual
Record your raw data in a data table. It should look something like the table below, though your values
may vary considerably.
Temperature (oC)
Gauge Pressure (bar)
Hot Bath
48.2
0.8
Room
22.3
0.69
Ice Bath
0.2
0.57
Dry Ice
-65
0.25
Table 1: Gauge pressure and corresponding temperature measurements for a fixed-volume
pressure vessel filled with air.
1. Since the measurements you made were gauge pressure, we must adjust them by adding atmospheric
pressure. Assume that the atmospheric pressure in the room was 1.0 bar or 14.7 psi for today’s
measurements. Add this to the gauge pressure you recorded, and produce a table like the one shown.
Temperature (oC)
Gauge Pressure (bar)
Absolute Pressure (bar)
Hot Bath
48.2
0.80
1.80
Room
22.3
0.69
1.69
Ice Bath
0.2
0.57
1.57
Dry Ice
-65
0.25
1.25
Table 2: Absolute pressure, gauge pressure, and corresponding temperature measurements for a
fixed-volume pressure vessel filled with air.
2. Next, plot absolute pressure on the vertical axis versus temperature on the horizontal axis of a plot. Add
a best-fit line, and include the equation on your chart. See Figure #1.
P-T Plot for a Fixed-Volume Pressure Vessel
Absolute
Pressure (bar)
2.00
1.50
1.00
0.50
y = 0.0049x + 1.5705
R² = 0.9991
0.00
-100
-50
0
Temperature (oC)
50
100
Figure 1: Plot of absolute pressure versus temperature for a fixed-volume pressure vessel filled with air.
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Stevens High School AP Physics II Laboratory Manual
3. Determine the value of absolute zero (the temperature at which the pressure would extrapolate to zero)
implied by your data and analysis.
Using the above data and the plot, absolute zero is calculated to be -320 oC. Small variations in
temperature and pressure can make a big difference in your final value.
4. Calculate the percent error between your value and the accepted value of -273.15 oC.
With the above data, this is 17.2%.
5. Discuss multiple sources of error, including their anticipated magnitude.
The PVC you are using is rated to 280 psi gauge (19.3 bar). What temperature could
your pressure vessel tolerate before bursting? Neglect the fact that the PVC itself will weaken at high
temperatures.
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