012-04394C Thermal Expansion Apparatus
3
Introduction
Most materials expand somewhat 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.
For materials that are not isotropic, such as an asymmetric crystal for example, a can have a
different value depending on the axis along which the expansion is measured.
a can also vary somewhat with temperature so that 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 steel. These metals are
isotropic so that a need only be measured along one dimension. Also, within the limits of
this experiment, a does not vary with temperature.
Procedure
➀ Measure L, the length of the copper tube at room temperature. Measure from the inner edge
of the stainless steel pin on one end, to the inner edge of the angle bracket at the other end
(see Figure 1). Record your results in Table 1.
➁ Mount the copper tube in the expansion base as shown in Figure 2. The stainless steel pin
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.
➤ NOTE: Slide or push the tube to one side of
the slide support. Drive the thumbscrew
against the pin until the tube can no longer be
moved. Use this as your reference point.
➂ Use one of the provided
thumbscrews to attach
the thermistor lug to the
threaded hole in the
middle of the copper
tube. The lug should be
aligned with the axis of
the tube, as shown in
Figure 2, so there is
maximum contact
Bracket on tube
Dial Gauge Spring Arm
Stainless steel pin
Figure 2 Equipment Setup (Top View)
Slotted bracket
Thumbscrew
Figure 1 Measuring Tube Length
Experiment: Measuring the Coefficient of Linear
Expansion for Copper, Steel, and Aluminum
(2 pages)
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