PASCO TD-8579A COMPUTER-BASED THERMAL EXPANSION APPARATUS - Manual (Page 8)

012-07599C Computer-based Thermal Expansion Apparatus
5
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Introduction
Most materials expand when heated through a temperature range that does not pro-
duce a change in phase. The added heat increases the average amplitude of vibration
of the atoms in the material, which increases the average separation between the
atoms.
Suppose an object of length L undergoes a temperature change of magnitude
∆
T. If
∆
T is reasonably small, the change in length,
∆
L, is generally proportional to L and
∆
T. Stated mathematically:
∆
L =
α
L
∆
T;
where
α
is called the coefficient of linear expansion for the material.
Materials that are not isotropic, such as an asymmetric crystal for example,
α
can have
a different value depending on the axis along which the expansion is measured. The
coefficient (
α)
can also vary somewhat with temperature. Therefore, the degree of
expansion depends not only on the magnitude of the temperature change, but also on
the absolute temperature.
In this experiment, you will measure
α
for copper, aluminum, and brass. These
metals are isotropic, so it is necessary to measure
α
along only one dimension. Also,
within the limits of this experiment,
α
does not vary with temperature.
Figure 1: Measuring Tube Length
Experiment: Measuring the Coefficient of Linear
Expansion for Copper, Brass, and Aluminum
L = length
rotary
pin 1. With a measuring tape or
metric ruler, measure L, the
length of the aluminum rod,
at room temperature. Mea-
sure from the center of the
stainless steel ring (in the
groove of the small end
block), to the center of the
rotary pin at the other end
(see Figure 1). Record your
results in Table 1 in the Data
and Calculations section.
2. Insulate the rod and thermistor with
a slitted, tubular foam wrap. Slide
the foam wrap from underneath the
rod until the foam covers the
circumference of the rod. The
spring clamp should jut out from the
top of the foam slit (See Figure 2).
Figure 2: Insulating the rod
foam
spring clamp
retaining pin
rotary motion sensor
Procedure