Alabama Science in Motion
Heat Energy: Heat Transfer
Teacher Notes
Heat Transfer
Purpose:
The purpose of this laboratory activity is to compare the heat transfer for an unpainted or white
aluminum can and an aluminum can painted black to determine which has the greatest
temperature change. In addition, this change in temperature is related to the Entropy of each can.
Course of Study 2005:
Standard #5: Entropy, Bullet 1: Quantitative Relationship Between Temperature Change
and Energy
Lab Time: 30 minutes
Setup Time per Station: 3 minutes
Objectives:
Students will be able to…

use Temperature Probes to measure the change in temperature of two different colored cans
(unpainted and painted black) as they are heated and cooled.

use the Xplorer GLX to record and display the temperatures from both probes.

determine the initial and final temperature of the air in each can.

calculate the change in temperature.

compare the change in temperature for the air in the two cans and determine which can absorbed the
most energy during the heating cycle and which can cooled the fastest.

Relate the change in temperature to change in energy of the cans as well as the change in entropy of
the cans.
Considerations:
You will need several outlets or power strips to plug the light sources into.
The topic of entropy can be very difficult. One suggestion for this activity is to discuss question
5 prior to doing the lab. Allow the students to consider entropy according to the two following
definitions:
The American Heritage Science Dictionary - Entropy
A measure of the amount of energy in a physical system not available to do work. As a
physical system becomes more disordered, and its energy becomes more evenly
distributed, that energy becomes less able to do work. For example, a car rolling along a
road has kinetic energy that could do work (by carrying or colliding with something, for
example); as friction slows it down and its energy is distributed to its surroundings as
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Alabama Science in Motion
Heat Energy: Heat Transfer
heat, it loses this ability. The amount of entropy is often thought of as the amount of
disorder in a system. See also heat death.
From Holt Physics, 2006:
“The measure of a system’s disorder is called the Entropy of the system. The greater the
entropy, the greater the system’s disorder.”
Precautions

Caution should be exercised around incandescent light bulbs. Bulbs can break if they are
bumped and are hot after being lit for just a few minutes.

Encourage your students to use exactly the same procedure for each can so that heat loss by
radiation is the only uncontrolled variable.

Point out that a one degree temperature difference between two small cans would translate to
a large heat transfer rate over a large surface area like a roof.
Background:
The rate at which the two cans radiate thermal energy depends on several properties including
the area of the cans, the thickness of the walls, the difference in temperature of the air inside the
can and the outside air, and the emissivity of the surface. Assuming that all other factors are
equal, the can with the greater emissivity radiates thermal energy faster.
Surfaces that tend to be good ‘radiators’ also tend to be good ‘absorbers’. Surfaces that are poor
‘radiators’ tend to be good ‘reflectors’. The silver-coated reflective interior of a Thermos® bottle
is designed to reduce the loss of thermal energy by radiation.
Extensions
Optional: Cooling With A Fan
Repeat the experiment but put a fan next to the cans so the air blows equally on each of the cans.
Turn on the fan and begin recording data.
Sample Data
The screenshots show the temperature versus time graphs for the air in the unpainted can and the
black painted can undergoing the cooling cycle.
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Alabama Science in Motion
Heat Energy: Heat Transfer
Unpainted can, initial temperature
Unpainted can, final temperature
Black can, initial temperature
Black can, final temperature
Answers:
Data
Temperature Probe #
Black heating
White heating
Black cooling
White cooling
Maximum
Temp (˚C)
28.5
25.4
28.0
25.0
Minimum
Temp(˚C)
20.2
20.4
26.5
24.5
Change in
Temp(C ˚)
8.3
5.1
1.5
0.5
Calculations
Calculate the change in temperature of the air in both cans.
Answers to Questions:
1. Which can had the greatest temperature change?
The air in the black painted can cooled down the most in the fifteen minutes.
2. What does this change in temperature tell you about the change in Energy?
There is a change or transfer of energy.
3. While the cans are cooling, which processes transfer heat? Which process do you think is
dominant?
Convection, conduction and radiation. Radiation is dominant.
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Alabama Science in Motion
Heat Energy: Heat Transfer
4. When a can is cooling, does it cool faster at the beginning of the experiment or toward the end
of the experiment? Why?
The can is cooling down faster at the beginning of the experiment. Newton’s Law of Cooling
describes the fact that things tend to cool faster when the difference in temperature between the
object and its environment is greatest.
5. Entropy may be thought of as the organization or order of Energy within a system. From Holt
Physics, 2006, “The measure of a system’s disorder is called the Entropy of the system. The
greater the entropy, the greater the system’s disorder.” Consider the energy changes in each can
WHILE BEING HEATED. Which can underwent the greatest change in order? Which can
underwent the greatest decrease in entropy WHILE BEING HEATED?
The can with the greatest temperature change underwent the greatest change in order. The
black can should have absorbed the most energy indicated by the greatest decrease in
temperature. The black can also had the greatest DECREASE in Entropy. As the black can
absorbed more energy, the air molecules become more ordered, their collisions are increasingly
frequent and less random.
Alternative predictions:
In which metal can would the air cool down the most in fifteen minutes: aluminum unpainted, or
aluminum painted black?
The air in the black painted can would cool down the most in fifteen minutes of cooling time.
Sketch your graph of temperatures versus time. Include units and labels for your axes. (See
Sample Data.)
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