Physics 1B
· THERMAL PROPERTIES AND HEAT TRANSFER ·
Rev. 3-AH
Introduction
This material corresponds with Hecht 2 nd Ed. Chapters 12 and 13. We will explore some
concepts in temperature and properties of materials as they change temperature. We will also
explore different modes of heat transfer. You will need to read the lab ahead of time and answer
all six Pre-Lab Homework questions on a separate piece of paper to be turned in at the
beginning of lab.
It is a good idea to read all the steps in each part before you start. Make sure that everyone in the
group has a chance to use the hands-on items at each station. In this lab you will be working
with some potentially dangerous materials. Read and observe the warnings below. Each student
must answer all the questions and record any observations before the end of the lab period.
Material in this lab has been adapted from Sokoloff, Real Time Physics.
Precautions and Warnings
Working with cryogenic liquids (liquid nitrogen):
Cryogenic liquids, liquefied gases with temperatures below –73 °C, and their boil-off vapors
rapidly freeze human tissue. Cryogenic liquids also produce large volumes of gas when they
vaporize and may create oxygen-deficient conditions.
• Use insulated gloves and eye protection at all times.
• Minimize boiling and splashing by slowly lowering objects into the cryogenic fluid.
• Avoid clothing that can trap spilled liquid. If skin contact with a cryogenic liquid occurs, do
not rub skin. Instead, place the affected part of the body in a warm (not hot) water bath.
Working with the propane torch:
•
•
•
•
You will be using a propane flame. The flame is very hot. It will BURN YOU!
Do NOT point the propane torch at yourself or anyone else.
The person holding the object being heated should always wear protective gloves.
When you are finished using the torch, turn it OFF. If you are not sure how to do this, ask
your TA before you turn it on.
© UCSD-PERG (2001)
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Physics 1B
· THERMAL PROPERTIES AND HEAT TRANSFER ·
Rev. 3-AH
Experiment A: Expansion of a Ball and Ring
Pre-Lab Homework:
A circular iron plate has a coefficient of linear expansion of 10-5 K-1. At 20 °C it has a circular hole at its
center with a radius of 2 inches. The plate is then heated to 40 °C.
1.
Predict the radius of the hole after heating: will it increase, decrease or remain the same?
2.
Calculate the numerical value of the radius at 40 °C.
Questions:
A1. At this station you will find a ball and ring (Fig. 1) and a blowtorch.
The ball and ring are made of the same metal. Does the ball fit
through the ring when they are both at room temperature?
A2. Now you will experiment with the propane blowtorch to observe
what happens when you heat up the metal ball and ring. BE
CAREFUL! You need to heat them for only 10 seconds. Write
down your observations when you heat just the ball, just the ring, and
both together.
A3. Do your observations agree with the prediction you made in
Pre-Lab #1?
A4. Place all hot objects on the hot plate.
Fig. 1: Metal ball and ring.
Experiment B: Volume, Pressure, and Temperature
Pre-Lab Homework:
3.
Predict what you think will happen if you dip an air-filled balloon into liquid nitrogen at a
temperature of approximately 77 K = –196 °C.
Questions:
B1. Now you will do this experiment by CAREFULLY and SLOWLY lowering a balloon into
liquid nitrogen and then CAREFULLY lifting it out using the tongs provided. Write down
what you observe.
B2. Does this agree with your prediction? Explain why you think your prediction was correct
or incorrect.
B3. Be sure to clean up any mess from things that have been dipped in the liquid nitrogen (such
as balloon shards or flower petals).
© UCSD-PERG (2001)
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· THERMAL PROPERTIES AND HEAT TRANSFER ·
Physics 1B
Rev. 3-AH
Experiment C: Conduction, Convection, and Radiation
Pre-Lab Homework:
4.
5.
6.
Suppose you have a cup of hot coffee (or tea, chocolate, or water). You place this cup on a table
and let it sit for a very long time.
(a) How cool does the coffee get?
(b) Where does the heat go?
(c) Does the rate at which the coffee cools stay constant, or change as it cools?
(d) Make a graph of what you think will happen to the temperature of the coffee over time.
(Hint: Time on the x-axis, temperature on the y-axis.) Be sure to clearly indicate initial
temperature and room temperature on your graph. How is the answer to part (c) shown on
your graph?
Suppose you have two Styrofoam coffee cups, one with a lid and the other without a lid. Your two
coffee cups are filled with coffee, and you put the lid on one cup. You set these two cups on a
table.
(a) Which cup of coffee do you think will cool faster, the cup covered with its lid, or the cup
without a lid?
(b) Why do you think the cup you picked will cool faster? (Try to explain using conduction,
convection, or radiation, if you can).
Suppose you have two coffee cups, one cup is Styrofoam with a lid and the other is a metal cup
with a lid. Your two coffee cups are filled with coffee, and you put the lids on both cups. You set
these two cups on a table.
(a) Which cup of coffee do you think will cool faster, the Styrofoam cup covered with its lid, or
the metal cup with its lid?
(b) Why do you think the cup you picked will cool faster? (Try to explain using conduction,
convection, or radiation.)
Materials and Procedure:
1. For this experiment, you will work in groups of two. You will use the following materials:
• Graduated cylinder
• Watch, clock, or timer
• Colored tape
• One thermometer per group of two students
• One cup per group of two students (choose from: Styrofoam with lid, Styrofoam without
lid, metal with lid, metal without lid, or Thermos cup with lid)
2. Record the type of cup you have in your lab notebook.
3. Measure 75 mL of tap water and pour it into your cup. Mark the water level on the cup with
a piece of colored tape. This is your “fill line.”
4. Dump out the tap water and dry out your cup.
5. Quickly fill the cups to the fill line with hot water. Put the lid on (if your cup has a lid) and
quickly place the thermometer in the cup.
6. Record the initial temperature of the water and take readings every 30 seconds for 5 minutes
for a total of 11 readings.
7. Feel the temperature of your cup by touching the outer surface at some point while you are
taking data. You should also try to feel the other types of cups that the other groups are
working on.
8. Repeat steps 4-6, this time taking readings for 10 minutes.
© UCSD-PERG (2001)
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Physics 1B
· THERMAL PROPERTIES AND HEAT TRANSFER ·
Rev. 3-AH
Experiment C (continued):
Questions:
C1. Graph the data you acquired on the same graph. See Pre-Lab #4 for what the graph should
look like. Be sure to label the axes and use either different colored ink or symbols to
distinguish between the two trials.
C2. Does your data from the two trials agree? Which trial do you think was more accurate?
Why?
C3. When you have finished graphing at your lab table, graph your 10-min data on the large
piece of graph paper that your TA has set up on the easel.
C4. By looking at the class data, which cup has a slower rate of cooling? How do you know?
(i.e., What property of the graph tells you this?)
C5. Which mode of heat energy transfer (conduction, convection, or radiation) is most affected
by covering the cup? How do you know — what are you using to make your decision?
C6. Which mode of heat energy transfer (conduction, convection, or radiation) is most affected
by using different types of cups (metal vs. Styrofoam vs. Thermos)? How do you know?
How does this relate to your observations when you felt the cups?
C7. Do these results agree with your predictions in Pre-Lab questions 4-6?
© UCSD-PERG (2001)
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