- University of Virginia
- Physics Department
A Physical Science Activity
2003 Virginia SOLs
- understand the mechanism through which thermometers record temperature;
- study various types of thermometers, including the mercury/alcohol thermometer,
the Galileo thermometer and the bimetallic thermometer.
Discrepant Event-Building an Air Thermometer
- Clear flask or bottle
- Rubber stopper to fit bottle, with hole in center
- Rigid plastic tubing to fit hole in stopper, 24" long (glass tubing can
be used, but it is dangerous)
- Food coloring
- Sealing wax or paraffin
- Scotch tape
- Cardboard strip, 10"x 2" (poster board or heavy paper will also work)
- Alcohol thermometer
There are two possibilities to make a thermometer that are similar. The normal
alcohol thermometers that we use contain alcohol with red coloring inside an
enclosed glass tube. Because the glass tube is enclosed, atmospheric pressure
does not affect the temperature measured. If the glass tube is open at the top,
rather than closed, then atmospheric pressure can affect the height of the alcohol
column thus affecting the reading. It is easier to build the later thermometer,
but it is accurate only over short time periods when the atmospheric pressure
is not changing.
- Place the tubing through the hole in the stopper. Be very careful doing
this if you are using glass tubing, because it is too easy to break the tubing
and stick glass in your hand. Use cooking oil as lubricant to make it easier
to put the tubing through the hole.
- Color ½ pint water with dye or food coloring. Pour this into the glass
bottle so that it is about ¼ full. It would be best if the water had already
reached room temperature.
- Place the stopper into the flask so that it makes a tight fit. The tube
end should be in the liquid and almost touching the bottom. Use the colored
water to fill the tube through the open end. Try to get the liquid to the
bottom of the tube to replace the air. You may have to tilt the flask to do
- Adjust the liquid level in the tube by loosening or tightening the stopper
until the level is about halfway up the exposed portion of the tube above
- Use the wax to seal the tube to the stopper and the stopper to the bottle.
- Cut three slits on the cardboard according to the diagram and slide it
on the tube above the stopper.
If you used room temperature water in step 2, you may now
mark the water level on the cardboard and note that this temperature is
room temperature that you have measured with a regular thermometer. If you
have not used room temperature water, you may have to wait a few hours until
the thermometer has reached thermal equilibrium with its surroundings.
Then record the air temperature with the thermometer. Mark the level of
liquid on the cardboard as this temperature.
- Place both the alcohol thermometer and your constructed thermometer in
a new temperature; for example, in a tub of water at a much higher temperature.
Make sure the water does not shoot out the top. If it does, you will need
a longer tube.
- Mark this new temperature on the cardboard.
- If possible, repeat this a third time in a new temperature setting, for
example in a refrigerator. Remove the cardboard from the glass tubing and
measure the distances between the different temperature markings. From this,
you can create an entire temperature scale; you have built an air thermometer!
A thermometer is a device used to measure the temperature of a system. When
a thermometer is in thermal equilibrium with the system, it measures its own
temperature as well as that of the system. The most common thermometer utilizes
a liquid, either mercury or alcohol. A glass bulb, filled with this liquid,
is connected to a glass capillary tube. When heated, the liquid expands from
the bulb into the capillary tube, so that the change in temperature corresponds
with the change in height of the liquid. Mercury is commonly used because there
is a wide temperature range at which it is liquid: from -38.9 °C to 356.7°C.
recently, alcohol thermometers have supplanted the use of mercury thermometers
in schools because of dangers associated with mercury. If you use a mercury
thermometer in the experiment, be especially careful that it does not break.
There are other, more complex types of thermometers as well. A Galileo thermometer
applies the fact that liquids expand faster with increasing temperature than
do solids. It is made of a column of fluid that contains solid spheres with
a density close to that of the liquid. If the sphere's density is less than
the liquid, it will float; if it is greater than the liquid, it will sink. As
the temperature increases, the liquid will expand faster than the solid and
the liquid's density will decrease at a quicker rate, so that the spheres will
eventually sink. Each sphere in a Galileo thermometer is a specific density
so that it will sink at an exact temperature, thus displaying the temperature
of its surroundings. The photo at the left is of a Galileo thermometer, which
are no longer commonly used.
A third type of thermometer, a bimetallic thermometer, is used in household
applications such as the thermostat. This thermometer is made of two strips
of different types of metal which are sandwiched together and rolled into a
coil. The metals expand at different rates with an increase in temperature,
causing the coil to either wind or unwind. A pointer connected to the bimetallic
coil indicates the temperature.
Note that the thermostat may have a mercury bulb inside to act as a switch.
MERCURY IS POISONOUS AND THE STUDENTS SHOULD NOT BE ALLOWED TO HANDLE THE THERMOSTAT.
for a description of the element mercury and how dangerous it can be. Most schools
no longer use mercury thermometers for this reason, and your school system may
not allow even a thermostat containing mercury inside the bulb to be in the
school, although they probably use thermostats in the heating/cooling system
that have mercury inside them. This activity is quite safe as long as the students
are not allowed to handle the thermostat. If by some accident, the mercury bulb
is broken, everyone should immediately move away. It should be safe to mount
the thermostat on a board using screws. The board can be a convenient size,
say 10" x 10", so that it will stay in one place. The thermostat needs
to be in the vertical position. There are thermostats available that do not
use mercury. One that we found is White-Rodgers brand Model 7200. This can be
bought at a home store such as Lowe's.
To print out the Student Copy only, click
- Alcohol thermometer
- Ice bath (600 mL beaker with ice and water)
- Optional: thermostat (Honeywell tradeline T87F 2873). Go to a building
supply company (like Lowe's) and purchase the cheapest (heat only) thermostat
you find. It should cost about $10. You can also purchase a heat/cool thermostat
which will have two bimetallic strips inside, one for heat and one for cooling.
- Observe the temperature initially on the alcohol thermometer. Then place
the alcohol thermometer in the ice bath. Observe and write down the indicated
temperature every minute.
- Observe how long it takes for the thermometer temperature to reach equilibrium.
- Examine the bimetallic thermometer in the thermostat. If the thermostat
has a mercury bulb inside, students should be very careful with the thermostat.
The thermostat should be mounted vertically on a firm location like a board
so students can observe it, but not handle it. Teachers should read the danger
warning about mercury in the Background Information. Put the thermostat in
a cool area (refrigerator, in front of an air conditioner vent, or blow air
over a container of ice) and observe what happens. Place it in a warm area
and observe what happens. Blowing hot and cold air from a hair dyer may be
a good option.
To print out the Data Sheet only, click
- How long did it take for the thermometer to record the equilibrium temperature?
What happened in the time it took for the reading to be accurate?
- How can the air thermometer accurately record temperature? Describe its
aspects that are similar to those of an alcohol thermometer.
- Why do liquids expand at a faster rate than solids? How does this help
a Galileo thermometer record temperature?
Students with Special Needs
All students should be able to participate in this activity.
Click here for further
information on laboratories with students with special needs.
Fill out data sheet during activity.