PASCO TD-8578 THERMAL EXPANSION APPARATUS User Manual
Page 6
012-07114D
Thermal Expansion Apparatus
3
Introduction
Most materials expand when heated through a temperature range that does not produce 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 = αL ∆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.
α can also vary somewhat with temperature. Therefore, the degree of expansion depends
not only on the magnitude of the temperature change, but on the absolute temperature as
well.
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.
Procedure
➀ Measure L, the length of the copper tube at room temperature. Measure from the outer edge
of the stainless steel ring on one end, to the outer edge of the stainless steel ring at the other
end (see Figure 1). Record your
results in Table 1.
➁ Mount the copper tube in the expan-
sion base as shown in Figure 2. The
stainless steel ring on the tube fits
into the slot on the slotted mounting
block and the bracket on the tube
presses against the spring arm of the
dial gauge.
➂ Use the capture spring on
the expansion tube to
attach the thermistor lug
somewhere in the middle
of the copper tube. The
lug will be aligned with
the axis of the tube, as
shown in Figure 2, so
there is maximum
contact between the lug
and the tube.
stainless steel ring
slotted mounting block
stainless steel ring
Figure 2 Equipment Setup (Top View)
contact indicator
Figure 1 Measuring Tube Length
Experiment: Measuring the Coefficient of Linear
Expansion for Copper, Brass, and Aluminum
L
thermistor
capture spring