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Physical properties of materials and systems can often be categorized as being either intensive or extensive, according to how the property changes when the size of the system changes. According to IUPAC, an intensive quantity is one whose magnitude is independent of the size of the system whereas an extensive quantity is one whose magnitude is additive for subsystems.
An intensive property does not depend on the system size or the amount of material in the system. It is not necessarily homogeneously distributed in space; it can vary from place to place in a body of matter and radiation. Examples of intensive properties include temperature, T; refractive index, n; density, ρ; and hardness of an object, η.
By contrast, extensive properties such as the mass, volume and entropy of systems are additive for subsystems.
Though it is very often convenient to define physical quantities to make them intensive or extensive, they do not necessarily fall under those classifications. For example, the square root of the mass is neither intensive nor extensive.