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Thermal expansion coefficient
Most solid materials expand upon heating and contract when cooled. The change in length with temperature for a solid material may be expressed as follows:
(Lf – Lo)/ Lo =al (Tf – To)
or
Δ L/ Lo =aΔT
Where Lo and Lf represent, respectively, initial and final length with the temperature change from To to Tf
. The parameter a is called the linear coefficient of thermal expansion; it is a material property that is indicative of the extent to which a material expands upon heating, and has units of reciprocal temperature [
(oC)-1or (K)-1].
The coefficient of volume expansion for solids and liquids (β ) is approximately 3 times the linear expansion coefficient (a)
Examples: Mercury
is liquid in the temperature range of -40° C to 357° C. Mercury expands as it gets warmer and its expansion rate is linear with the increase in temperature. This increase can be accurately calibrated and it becomes the basis of the mercury
thermometer
The expansion coefficient of water (ice) are not
at all typical! Water has the maximum density at 4 ° C. The volume of a particular amount of water increases both below and above 4 ° C. This is the reason why ice floats on water! The temperature of water at the bottom of a lake is usually around 4 ° C and the fish survive over a cold winter when the lake is covered with ice.
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