What defines the change in length per unit length per degree rise in temperature?

The definition of the change in length per unit length per degree rise in temperature is described by the coefficient of linear expansion. This property quantifies how much a material expands or contracts when the temperature changes.

When temperature increases, most materials tend to expand, and the coefficient of linear expansion provides a numerical value to express this relationship. It is typically expressed in units of inverse temperature (e.g., per degree Celsius or per Kelvin), indicating how much the length of a material will increase (or decrease) for each degree of temperature change, relative to its original length.

Specific heat is related to the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius, rather than to its change in length. The coefficient of conductivity pertains to the ability of a material to conduct heat, which is not directly related to the physical expansion of materials. Latent heat of fusion refers to the heat required to change a substance from solid to liquid at its melting point, which also does not pertain to length change with temperature. Thus, the coefficient of linear expansion is the appropriate concept that defines this thermal behavior in materials.