PHYSICS 124 LAB 9:
THE THERMAL COEFFICIENT OF LINEAR EXPANSION
GOAL:
In this lab exercise your goal is to measure the thermal coefficient of linear expansion for three
different metal rods.
Procedure
1.
The setup consists of a metal rod supported on one end by pins and on the other end by a
simple support so that it can expand. Steam can be generated and passed through the rod in
order to heat it. The temperature of the rod is measured by measuring the resistance of a
temperature-dependent resistance in a small clip attached to the rod. The instructor will show
how this is set up. The temperature of the rod can then be determined by looking up a value in a
table attached to the apparatus. The apparatus should be set up so that condensed steam (water)
drains out of the rods into a small beaker or pan. Blocks of wood are useful, or you might use a
4 inch stack of paper towels if available instead of wood blocks. Gloves or paper towels are
useful to handle the hot rods after measuring their expansion.
a)
Determine the length of each rod by using the meter stick. Leave the rods on the table
away from the apparatus so that they remain cool, at room temperature. Room temperature can
also be determined from the electronic thermometers on your lab table.
b)
One by one, you will measure the expansion of the three rods, so the procedure will be
the same for each one. Start by putting the rod on the apparatus, with the pin in the proper slot.
Notice how the micrometer dial turns when the rod expands by pressing the micrometer pin with
your finger. When you begin heating, the dial may move more that one turn, and may move in a
clockwise or counterclockwise direction, so check this before you start heating.
c)
The steam is generated by a small device similar to a “hot pot” which should be filled
about half-way with distilled water (from the jugs). This is done to prevent buildup of mineral
deposits in the hot pot. Remember that steam can burn you! So be careful handling the hose and
metal rods once they get hot. You might want to start the pot heating right at the beginning of
the lab, while the instructor goes over the experiment.
d)
When you are ready to heat the rod, note the position of the micrometer dial or set the
dial to zero by rotating the outside rim by hand. Using a glove, attach the hose (once it has steam
coming out of it) to the rod and watch the dial rotate. You should be measuring the temperature,
and will notice a rapid rise at first, and then it will stabilize between 90oC and 100oC. Once the
temperature stabilizes, record the values of final temperature and change in length. Calculate the
change in temperature T and the coefficient of thermal expansion.
41
Physics 124 - Data and results for Lab 9
Type of rod
Name _____________________________
Aluminum
Copper
Steel
24.0 x 10-6 (1/oC)
16.8 x 10-6 (1/oC)
13.4 x 10-6 (1/oC)
Initial length Lo
Initial
micrometer
setting
Final
micrometer
setting
L
Initial
Temperature
To (oC)
Final
Temperature
T (oC)
T = T - To
(measured)
(accepted
handbook value)
42