The Measurement of Expansion of Solids. The first demonstration in] FIG. 1 [
proves that when the temperature of a solid increases, the solid expands but that demonstration gives no definite idea of the amount of this expansion. The amount of expansion varies with different substances, but for a given solid it is directly proportional to the temperature.
Demonstration. - Set up the apparatus shown in Fig. 2, in which the copper tube AB is fixed to the support at the point A, and note both the temperature of the room and the reading of the pointer. Cover the copper tube with a non-conductor, attach a rubber tube to either end, and send steam through it from a boiler. After the steam has been coming through the tube freely for some time, take a second reading of the pointer and call the temperature of the steam 100° C.
From the above readings the changes in length of the tube and the changes in its temperature can be found. Then we can write the following:
length for 1 degree, and this is the coefficient of linear expansion. In general: The new length = The original length + The increase in length,
or L' = L + k t L
or L' = L (1 + kt)
in which L is the length of the rod at zero, L' is its length at the temperature t°, and k is the coefficient of linear expansion.
