When materials are heated, they expand. The degree of expansion with temperature is the coefficient of thermal expansion
, CTE. The coefficient of thermal expansion is shown by the expansion of a body in all three dimensions. The coefficient of thermal expansion depends on the material and is expressed in parts per million (ppm) relative to Kelvin (ppm/K). For quartz
, the coefficientof thermal expansion is 0.6 x 10exp-6 per Kelvin, for copper
it is17 x 10exp-6 per Kelvin, and for lead
it is29 x 10exp-6 per Kelvin.
There are also materials that contract rather than expand with increasing temperature. This is called contraction. An example of this is water at temperatures between 4 °C and 0 °C.