Number density

As particle density ( particle number density, particle or particle concentration ) is defined as the number of particles (molecules, dust particles, etc.) per volume ( unit m- 3):

For mixtures, the particle density can be meant as a whole or only for a certain type of particle.

Attention: the particle density should not be confused with the amount of substance which also has the formula n characters.

Application

The particle has a wide range of applications in physics, because many variables can be expressed by them. For example, the mass or charge carried by the individual particles, so the bulk density or charge density, straight from the particle ( the carrier ) can be derived. In gases, for example, the pressure and the density depends almost linearly on the particle.

As a mere indication of the particle concentration provides handy numbers when the concentrations are very small, and is therefore used in the reaction kinetics of trace substances and astrophysics for the particle density in space. For higher concentrations are usual data in mol / ℓ, the conversion factor is the Avogadro constant.

Examples

• Thermodynamic state variable