## Quick Reference

**Linear expansivity** is the fractional increase in length of a specimen of a solid, per unit rise in temperature. If a specimen increases in length from *l*_{1} to *l*_{2} when its temperature is raised θ°, then the expansivity (α) is given by: *l*_{2} = *l*_{1}(1 + αθ). This relationship assumes that α is independent of temperature. This is not, in general, the case and a more accurate relationship is: *l*_{2} = *l*_{1}(1 + *a*θ + *b*θ^{2} + *c*θ^{3}…), where *a*, *b*, and *c* are constants.

*l*_{2} = *l*_{1}(1 + αθ).

*l*_{2} = *l*_{1}(1 + *a*θ + *b*θ^{2} + *c*θ^{3}…),

**Superficial expansivity** is the fractional increase in area of a solid surface caused by unit rise in temperature, i.e. *A*_{2} = *A*_{1}(1 + βθ), where β is the superficial expansivity. To a good approximation β = 2α.

*A*_{2} = *A*_{1}(1 + βθ),

**Volume expansivity** is the fractional increase in volume of a solid, liquid, or gas per unit rise in temperature, i.e. *V*_{2} = *V*_{1}(1 + γθ), where γ is the cubic expansivity and γ = 3α. For liquids, the expansivity observed directly is called the **apparent expansivity** as the container will also have expanded with the rise in temperature. The **absolute expansivity** is the apparent expansivity plus the volume expansivity of the container. For the expansion of gases, see Charles’ law.

*V*_{2} = *V*_{1}(1 + γθ),

http://www.kayelaby.npl.co.uk/general_physics/2_3/2_3_5.html Values of the expansivity of selected liquids and solids at the NPL website

**From:**
expansivity
in
A Dictionary of Physics »

*Subjects:*
Physics.