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TOPS Physics - Thermodynamics
Determination of absolute zero
Absolute zero is the lowest possible temperature, that at which all molecular motion
stops. Since pressure is dependent upon molecular motion and varies linearly with
temperature we can use the pressure of a container of gas at various temperatures to
extrapolate a line to determine the temperature at which pressure would be zero.
Purpose:
To determine absolute zero.
Equipment:
Vernier Gas Pressure Sensor
Vernier LabPro Interface
Apple iBook computer
Aluminum Air Chamber Assembly with
temperature sensor
(3) water containers
Cautions:
This equipment is delicate. Everything should go together with the lightest of touches.
Do not force anything!
You may find that some of the setup procedure has already been done for you. Check
each step to make sure that it is done properly. The success of your work depends upon
correct setup!
Procedure to set up the pressure sensor
1. Prepare three containers of water, one at room temperature, one with hot tap water,
and one with ice.
2. Connect the tube from the aluminum air chamber to the pressure sensor.
3. Connect the gas pressure sensor to the “CH 1” port of the LabPro interface.
4. Connect the temperature sensor to the “CH 2” port of the
LabPro interface.
5. Connect the LabPro interface to the iBook computer with the
USB cable.
6. Plug the LabPro sensor into a power outlet. After a short pause,
it will beep merrily.
7. Plug the iBook computer in with its power adapter.
8. Turn on the iBook and wait for it to boot up.
9. Log on to the computer with the username “student” and
password “student”.
10. Launch the “Absolute Zero” Activity by double-clicking it.
Pressure
Sensor
Aluminum
Air Chamber
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Data Collection:
Important: Read steps 1-11 completely before performing them
1. Click on the collect button to start data collection
2. Immerse the aluminum air chamber and temperature probe in the ice water bath.
3. Watch the temperature value. It will decrease as the gas in the aluminum air chamber
cools.
4. When the temperature stabilizes (does not change for 30 seconds or so) The
temperature may switch back and forth between two values repeatedly. This is
normal and does not indicate that the temperature is changing.
5. Click on the Keep button.
6. Enter a point number and click on OK. Number the data points 1, 2, and 3.
7. Immerse the aluminum air chamber and temperature probe in the room temperature
water.
8. Repeat steps 3-6.
9. Immerse the aluminum air chamber and temperature probe in the hot water.
10. Repeat steps 3-6.
11. Click on the Stop button. You are through taking data.
Recording your data
Enter the data from the computer’s screen into this Data Table:
Data Point
1
Ice Water
2
Room Temp.
Water
3
Hot Tap Water
Pressure
(kPa)
Temperature
(C)
Computer Data Analysis
1. Click on the Linear Fit button (look for the “R=” button at the top of the screen)
2. A box appears. Look for the y-intercept value in the box. Write it here:
3. Click on the “X” in the box to close it.
4. Double-click in the graph window. The Graph Options window appears
5. Click on Axes Options.
6. In the left hand column (y-axis) change the “Bottom” values to -300.
7. In the x-axis box at the bottom, change the “left” value to -10.
8. Click the Done button.
9. Click on the Linear Fit button (look for the “R=”) again.
10. Notice that, at zero pressure, the line will indicate the temperature associated with
absolute zero. That is how the value for absolute value is determined.
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Graphical Data Analysis
1. On the attached graph paper, plot the temperature data. Note that the temperature is
on the x-axis of this graph.
2. Draw your best-fit straight line through the data points.
3. Extrapolate the best fit line to the left until it crosses the P=0 line.
4. Determine the temperature at P=0, write the value here:
Questions:
1. The accepted value for absolute zero is -273 o C. How well did your value correlate
with the accepted value?
2. Would the effect of small errors in measurement be magnified in finding absolute
zero? Explain why or why not.
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3. How could the experiment be modified to improve the accuracy of its results. You
need not limit yourself to the equipment at hand.
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Teacher Reference Pages
Introduction:
The classic method of determining absolute zero depends upon the kinetic theory of
gases. The pressure of a gas is caused by the momentum of the gas molecules, so at
absolute zero where the kinetic energy of the molecules is zero the pressure will be zero.
This method assumes that the gas in question is ideal with a linear relationship between
temperature and pressure at constant volume.
Experimental goals:
After completing this experiment, students will be able to describe the method and
practice of determining absolute zero. They will be able to determine the value of
absolute zero by creating and interpolating a graph of temperature/pressure data. They
will be able to evaluate the accuracy of their measurements and cite possible sources of
errors in the experiment.
California Science Standards addressed in this laboratory activity:
Academic:
3(a) Students know heat flow and work are two forms of energy transfer between
systems.
3(c) Students know the internal energy of an object includes the energy of
random motion of the object's atoms and molecules, often referred to as thermal
energy. The greater the temperature of the object, the greater the energy of motion
of the atoms and molecules that make up the object.
3(g) Students know how to solve problems involving heat flow, work, and
efficiency in a heat engine and know that all real engines lose some heat to their
surroundings.
Investigation & Experimentation:
1(a) Select and use appropriate tools and technology (such as computer-linked
probes, spreadsheets, and graphing calculators) to perform tests, collect data,
analyze relationships, and display data.
1(b) Identify and communicate sources of unavoidable experimental error.
1(c) Identify possible reasons for inconsistent results, such as sources of error
or uncontrolled conditions.
1(d) Formulate explanations by using logic and evidence.
1(l)Analyze situations and solve problems that require combining and applying
concepts from more than one area of science.
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Equipment:
Vernier Gas Pressure Sensor
Vernier LabPro Interface
i-Book computer
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Key words: temperature, pressure, volume, absolute zero
Procedure notes:
Each lab group needs a minimum of 2 students
Aluminum Air Chamber Assembly with
temperature sensor
(3) water containers
Students must be patient while waiting for the gas in the aluminum air chamber to reach
equilibrium. This is important to getting good data.
Answers to questions:
1. The accepted value for absolute zero is -273C. How well did your value correlate
with the accepted value?
Typically, student errors might seem large. Values from -350 to -200 are to be
expected.
2. Would the effect of small errors in measurement be magnified in finding absolute
zero? Explain why or why not.
Since the data is extrapolated quite a large distance from the collected data, small
errors in that data will result in large errors in the calculated results.
3. How could the experiment be modified to improve the accuracy of its results? You
need not limit yourself to the equipment at hand.
The accuracy of the experiment could be greatly improved by taking data over a wide
temperature range. Student suggestions might be to use boiling water to collect data
at higher temperatures and to use dry ice or liquid nitrogen to collect data at lower
temperatures. Any of these suggestions would result in a wider range of data that is
more likely to be extrapolated to yield an accurate value for absolute zero
References
Vernier equipment guide
California Science Standards
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