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Science in the Lab
Radish | Temperature | Brine
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Science at Home Photograms | Natural Fragrances About Women and Science Books and Links |
To understand that temperature scales can be arbitrary. To identify appropriate materials for the measurement of temperature by the thermometric properties of the material. To create temperature scales using a variety of "thermometers". To use a variety of representations to convert from the student constructed scales to a conventional scale. To identify appropriate representations for different types of data. To transfer the concepts of scale and calibration to other common scales such as PH and Barometric Pressure.
Background: This activity assumes that students have had prior
instruction in
several areas.
Multiple
Representations:
This activity assumes that the students are familiar with
representing
information in tabular form, graphical form, text or story form, simple
diagrams or pictures, and with a mathematical model depending upon the
math level of the student. Students that have completed some algebra will
be able to work with equations while students at the pre-algebra level
will approach the mathematical form as an operation that is performed to
help describe the event. A supplementary activity on multiple
representations is included to illustrate what is meant by multiple
representations and how any topic may be used to instruct students in the
use of these representations. Instructors will notice that the list of
representations might be expanded for higher
level students. For example, stylized diagrams such as ray diagrams,
field lines, and circuit diagrams could be added to the list.
Graphing and Scale
Interpolation:
Students should be able to read and plot a number on a
scale that is
between labeled scale values. For example, the student should be able to
read temperature to a fraction of a degree given a thermometer that is
marked with lines every degree. Students will be asked to create graphs
with their measured data. They will need to make decisions about
appropriate scaling.
Algebra:
The activity assumes the student has had elementary
algebra and
recognized the equation of a line y=mx+b. The instructor will need to
modify the
activity to exclude or simplify the sections that deal with the equation
of the graphed line. I have included one such simplification in a
supplementary section: Variable Relationships
The section on the digital thermometer does not assume
that the student
can read a simple circuit diagram. A pictorial description is included
next to the circuit diagram as an introduction to this type of
representation. The instructor may wish to include only one of the
diagrams depending on the experience of the students.
Annotation:
Students are directed several times through out this set
of activities
to
annotate a chart or diagram. The instructor will need to go over this
with students who are unfamiliar with the term. In most cases where the
student is asked to annotate, there is a diagram, graph, or table that the
student must interpret to find information (such as a conversion). The
annotation is a set to descriptions right on the chart showing an example
of how to use the chart. It is intended to be useful to the student as a
reference. It is also suitable for evaluation.
Introduction:
Temperature is the measure of the hotness or coldness of
an object or
substance. This can be accomplished (though not always recommended) to a
degree by touching the object. However, as one can notice on a cold day,
the feel of two objects outside in cold weather can be quite different
when they should be the same temperature. For example, touching a plastic
tool handle on a cold day can be done with bare hands without too much
discomfort, however a metal bar setting next to the tool handle will be
quite uncomfortable. If one wishes to communicate the coldness of the
objects, it is difficult to do unless the exact same situation is
available to the other person to touch.
In many situations it is useful to have a way of communicating the
hotness
or coldness of an object. For this reason we look for materials that
change an observable property as the material is heated up or cooled down.
This property is called a thermometric property. A record is then made of
this property as heat is added or removed. This record then becomes a
standard against which the hotness or coldness of other objects can be
compared. A variety of substances have these thermometric properties. We
will be looking at three types of thermometric properties, expansion,
changing electrical resistance, and color.
With each substance we will create this record (scale), calibrate it
with
standard records (scales), and use our newly constructed thermometers to
measure temperature. Part of the rational for constructing an unusual
thermometer is to help the student to separate the concept of adding or
removing heat (energy) from a particular scale (temperature). Heat added
to a material causes such changes as melting, boiling, expansion, etc.
When these changes are compared with a scale (any scale), we use the word
"temperature."This is just a convenient way of communicating
the hotness
or coldness of an object. Heat and temperature are very different things.
Procedure:
Qualitatively observe three types of thermometric
properties.
There should be three types of material present in the lab. Each type
will change a different physical property when heat is removed or added.
Physical properties that change when heat is added or removed are called
thermometric properties. The three types of change that we will observe
are color, resistance, and size.
LC Mylar Sheets which change color, thermistors (or common magnet wire)
which change resistance, and a variety of solids, liquids and gases that
change their size.
Students should observe how LC Mylar Sheets change when touched, or
immersed in cold water. Many students will recognize this as a common
property of certain paints and fabrics. I have found small toy cars,
pens, T-shirts, etc. that are dyed or painted with a special paint that
has thermometric properties. If a variety of products are available, the
students can compare how different products will have different color
changes or react to different temperature ranges.
A sample Thermistor should be available so that students can measure
changes in the resistance when heated with a hand or warm air. Long wire
should be soldered to the Thermistor and the thermistor attached to a flat
object to keep the small Thermistor wires from breaking.
A variety of things are suggested in the extension section as examples
of
expansion with added heat. The air thermometer with the clear soda straw
is an easily constructed example. Each student can make one and then
experiment with immersing the end in container containing water at a
temperature different than the room.
After each of the previous qualitative activities the student should
record observations about the changes in color, resistance, or size as the
temperature goes up or down.
Different Temperature
Scales:
Place the zero degree Fahrenheit and the zero degree
Celcius thermometers in a container of
water. Take
readings of both thermometers. Repeat for several different water baths
and ice water. Report the "Relationship" between values on the
two
thermometers in a variety of representational forms (picture, graph,
table, text, equation). The conversion equation (familiar to many
students) will be written from the best fit line on the graph.
Materials for Extension
Activities:
Evaluation:
Multiple representations of the relationship between
standard
Thermometer
readings and a newly constructed "Thermometer" will be
developed. The
students will be making 3 types of thermometers, an electronic temperature
probe, a bulb thermometer, and a color change thermometer strip. For each
(if possible), the students will use four different representations to
create a calibration report to allow readings on the new thermometers to
be converted to standard scales readings. The four representations to be
used are: text, table, picture or diagram, and graph. Students will
report which representations were more and which are less useful for each
new thermometer.
Students should be able to use the calibration reports to convert what
was
measured with the constructed thermometers to a conventional unit, zero
degrees Celcius or Fahrenheit.
Evaluation by portfolio or written/oral report will follow easily from
the
multiple representations of the calibration reports done in each section.
Process or lab (practical) exams can be created from the extensions.
Annotated calibration reports make nice references for the student as well
as an evaluation tool for the instructor.
Resources:
Standard Physics lab books.
You can collect quite a library of old lab books from used book stores.
I have several and find them excellent sources of "new" tricks!
String and Sticky Tape Experiments, Ed. by Ronald Edge, AAPT, One
Physics
Ellipse, College Part, MD 20740-3845, $24.00 (Members of AAPT receive a
20% discount.)
Experiments for all levels. These experiments can be made from very
inexpensive everyday items such as string, straws, paper cups, tape, etc.
TOPS Learning System modules on Temperature and Kinetic Model
These are Task Card Series. Each book consists of a number of task card
activities. The activities can be done with inexpensive on-hand items
much like String and Sticky Tape Experiments. Each book covers a
different general topic and includes teacher notes.
TI CBL system (call 1-800-TI-CARES)
TI has a Calculator Based Lab system. Here is a small and very versatile
piece of test equipment that may be easily taken to the field.
The Physics Teacher (A Journal of the American Association of Physics
Teachers)
This Journal is filled with ideas for the classroom. As a member of the
AAPT you are also invited to attend both local section meetings in the
fall and national meetings in the winter and summer.
Vernier Software, 2920 S.W. 89th St. Portland, Or. 97225 (503) 297-5317
This company sells computer based laboratory equipment and data analysis
software for both IBM and Mac systems. Their prices are very affordable.
Heat and Temperature, Tools for Scientific Thinking, available from
Vernier Software ($20)
This is an inquiry based curriculum to accompany a computer based lab.
Thermometric properties are properties of a material that
change as heat
is removed or added. In this first activity you are going to observe
three types of thermometric properties.
1a: Ball and Ring
Try to pass the ball through the ring with both at room temperature.
Then
heat the ring and try again. Explain what happened.
1b: A Flask of Water
A flask full of water and fitted with a stopper and tube is setting next
to a water bath. Immerse the flask in the hot water bath and observe any
change that occurs. Describe any change that you observed.
Both of these activities are examples of a particular thermometric
property; thermal expansion. Measured changes in volume or length can be
used to design a thermometer. List some common everyday items that have a
noticeable change in size with the adding or removal of heat.
2: Thermostrips
Select a thermostrip and note its appearance. Place your hand or a
warm
cup of coffee on the thermostrip. Describe any physical changes that you
observe.
The thermostrips change their color when heat is added or removed.
List
common everyday examples of this thermometric property.on
everyday examples of this thermometric property.
3: Thermistors
Note the physical appearance of a thermistor before and after warming it
with your hand. You should have difficulty observing a change. A
thermistor is a device that changes its electrical property, resistance
when heat is added or removed. To observe this, connect each end of the
thermistor to a one terminal of the multimeter provided. (The multimeter
should be set to measure resistance.) How does the resistance change as
the thermistor is warmed with your hand?
For each of the thermometric properties observed you should be able to
answer the questions:
"How does the object change as heat is added?" or "How
does
the object
change as heat is removed?"
Your answer to these questions is a description of the relationship
between the amount of heat added or removed and the thermometric property
of the object. At this time your description is qualitative. You have
described changes qualitatively, greater or smaller size or resistance and
different colors. To better describe the changes we will need to answer
the question how much does it change. This is a quantitative description.
With a quantitative description, we can compare how hot one item is to
another, we have a thermometer.
Thermistor as a Temperature Probe
Construction
A thermistor is a resistor that changes resistance with
temperature. When
connected to a resistor as shown below and the Voltage, Vout measured with
a meter, we have a simple circuit for an electronic thermometer, sometimes
called a temperature probe. If a digital multimeter is used to measure
the voltage as shown, then you have the makings for a digital thermometer.
As with all thermometer scales, you will need to calibrate this
thermometer by using a standard thermometer and creating some type of
reference chart.
This type of temperature probe is extremely useful in situations where
the
probe needs to be physically separated from the scale (meter) that is
read, remote sensing. For example a temperature probe might be located
outside an airplane in flight, inside a piece of electronic equipment, or
perhaps at the bottom of a river. In each case it would not be practical
to take a thermometer to that location and read it.
Follow the diagram below and construct your temperature probe. You
will
want to attach the thermistor to longer wires, and the longer wires to the
rest of the circuit. You will need to attach the Thermistor to the
resistor in such a way that good electrical contact is made. If you are
soldering, be careful that you do not get the thermistor too hot. Attach
wires as indicated. The thermistor must be free to be in contact with the
substance that you are using to measure the temperature. If this material
is a liquid, you will want to isolate the thermistor. You will need to
coat the probe to make it water-tight. Epoxy works well but must be used
with suitable ventilation. There are other products that will work as
well. I have used Plasti-Dip. Check with your local hobby and craft
store for other ideas.
Taking Readings:
To calibrate the temperature probe, we will use
water-baths at
different
temperatures and a standard thermometer, either Celsius or Fahrenheit.
Immerse both in the water-bath, being careful that the temperature probe
is no deeper that the water-tight coating will allow. Neither the probe
nor the standard thermometer should touch the container. Let them set in
the water long enough for the readings to stabilize. To calibrate your
thermistor you must measure the Voltage (Vout from you circuit) versus
Temperature (measured with an accurate thermometer). Record these values.
Change the temperature of the water and repeat several times. Make sure
that you choose water-baths that range from ice to as hot as is safe (near
boiling would be ideal).
Calibration with Multiple
Representations:
You should now have 4 different ways to compare the standard
temperature
in zero degree Celcius and the voltage readings for your temperature
probe.
Using the Calibrated Temperature Probe
Use your temperature probe to measure the temperature
(actually you
take a
voltage reading) of something which has an unknown temperature.
Use each of the following calibration representations to convert the
voltage reading to a standard temperature value. As you do this with each
representation you will find that some representations seem to work better
than others. For each representation, annotate it to include the method
that you use to convert the voltage to a temperature.
Which type(s) of representation was the least useful? Explain.
Which type(s) of representation was the most useful? Explain.
Introduction:
Thermal expansion is called a thermometric property
because the
relative
expansion of most materials indicates whether the material is gaining or
losing heat, that is, getting hotter or colder. Thermal expansion is
uniform enough that we can divide the change in length of something into
equal segments and call that a temperature scale like the Celsius
temperature scale.
The goal in this extension is to build, calibrate, and use a
water-thermometer to measure the temperature of an unknown water bath.
Make the Water-Thermometer
Insert a glass tube into the hole of a one-hole stopper.
Fit one end of
a long piece of clear tubing over the end of the glass tube that will be
on the outside of the flask. Fill the flask to the top at the sink, and
stopper the flask so that the water rises about 20 cm past the joint in
the clear tubing. You will use this joint as a reference point for
measuring the length of the water column as it rises or falls. Once you
have the water where it can rise or fall and be seen clearly, and the
stopper is snug in the neck of the flask, don't move the stopper until you
are finished.
Be sure you know why it is important that the stopper not be moved.
What
variables would be changed if the stopper were moved. When you are done
with the lab, try this and see what affect moving the stopper has.
Calibrathe the Water-Thermometer
In the Lab there are three large water baths maintained at
different
temperatures as indicated by the standard thermometers. These are
provided for you to calibrate your water-thermometer. Place the flask of
your thermometer in each water bath, and wait for the water in the tubing
to stop rising or falling. Be sure to immerse nearly the entire flask.
For each bath, put a mark at the level of the water in the tubing.
Measure the height of each mark above the reference point. Be sure to
note the temperature(zero degrees Celcius) of each of the water baths.
To use the water thermometer, we need to look at the relationship of
the
water column length to the Celsius Temperature. Finish calibrating by
reporting the relationship between water temperature off the standard
thermometer with the height of the water above the reference point.
Report this relationship in each of the following formats. (Optional) Students with the necessary math skills may
write the
equation
of a best fit line from the graph of the temperature vs. height. The
equation can then be used with the height of the unknown to solve for the
unknown temperature.
Use the Water-Thermometer
Measure the temperature (height of the water in the tube
above the
reference point) of the unknown water bath with your water thermometer.
Activity Supplement Analyzing Graphs A graph is a type of pictorial description of the
relationship of one
variable to another. The shape of the line can tell us whether the
position is increasing or decreasing as the time instant increases. The
specific dependence of one variable on another is called the
relationship
between two variables.
Consider the three distance vs. time graphs below. All three graphs
show
that the distance is increasing as time increases. However, it is clear
that the relationship between distance and time is not the same in each
case.
What is needed, therefore, is a better way of expressing this
relationship. For this, we need to recall some algebra. Each of the
lines in the graphs above represent some general line shapes that can be
described with an equation. Let's begin with a straight line graph.
Recall the equation of a straight line as y=mx+b where:
Exercise 1 Use the Distance vs. Time graph below to answer the questions. (a) Find the slope of the line.
(b) Explain why it was not correct to use the point (0,0) in
calculating
the slope.
(c) Find the vertical axis intercept.
(d) What is the vertical axis variable? Assign a 1 letter equation
variable to it.
(e) What is the horizontal axis variable? Assign a 1 letter equation
variable to it.
(f) Write the equation of the line. (Be sure you do not use the
equation
variables x or y in your equation. The graph is not a y vs. x graph.)
This method for finding the equation that describes the
relationship
between two variables works fine for straight line graphs. However, there
are many times that the relationship is not linear (a straight line). In
these cases you will need to linearize the graph first. The
process of
linearization is used to get a straight line (linear) graph from which an
equation can be written.
You should recall several standard graph shapes from algebra, and their
general equation forms.
We have already dealt with the linear graph. Let's look
at the nonlinear
graphs. Note that each of the equations has the letter "k".
This is a
constant, similar to the slope constant, m, in the linear equation. The
constant k is not the slope of the curved line. In fact, it can't be the
slope because the slope of the line is changing. Only a linear graph has
a constant slope. What the k does is determine how great or little the
curving is.
Exercise 2
(a) Graph both equations below on the graph grid
provided. Do each
equation in a different color and label the curves. Even though the
graphs are not linear, it is common to refer to the graphed curve as a
line.
(b) Each equation has a different value of k. How does the k value
change the shape of the graph?
Now let's linearize the graph so that the linear equation can be used.
Exercise 3
We will use only the equation (a) Now take each value of x in the left column and
square it. Put this
value in the column labeled x2. You choose to square it
because the
shape
appears similar to the (b) You will now plot a new graph of y vs. x2. Label the
vertical
axis
y. Label the horizontal axis x2. Title the graph. You should
come
up
with a straight line. If you don't, the graph may not be a Question B.2.1
You are provided with the following data and asked to analyze the
information to determine the relationship between Pressure and Volume.
(a) Look at the data below and decide which variable should be
represented on the horizontal axis. Explain your reasoning.
(b) Graph the following data on a separate piece of graph paper:
(c) Use the method of linearization to find the equation describing
the
relationship between pressure and volume. You may need to make another
graph. If so, use another piece of graph paper. Show your equation
below.
(d) Annotate the graphs that you made to complete the linearization
task.
The annotations should include comments about the linearization process
that refer to the graph.
Question 2
Write a paragraph or two describing the linearization process that you
used to find the relationship between pressure and volume. Make the
description appropriate to a junior high science student.
Question 3
Explain in your own words what is meant by the term
"relationship" as
used
in the questions above.
(c) Write the equation of the straight line for the y vs
x2
graph.
Remember that you plotted x2 on the horizontal axis and not x.
Be sure
that you measure the slope and include that value in the equation. You
should have an equation that looks like Rural Girls in Science Program |
shape.