What is “Number density” ?
In physics, astronomy, chemistry, biology and geography number density is an intensive quantity used to describe the degree of concentration of countable objects (particles, molecules, phonons, cells, galaxies, etc.) in the three-dimensional physical space. Areal number density (number of entities per unit surface area) and linear number density (number of entities per unit length) are defined analogously. Population density is an example of areal number density. The term number concentration (symbol: C) is sometimes used in chemistry for the same quantity, particularly when comparing with other concentrations.
Here it is assumed that N is large enough that rounding of the count to the nearest integer does not introduce much of an error, however V is chosen to be small enough that the resulting n does not depend much on the size or shape of the volume V.
Similar expressions are valid for electric charge or any other extensive quantity associated with countable objects. For example, replacing and (charge of each object) in the above equation will lead to a correct expression for charge.
The number density of solute molecules in a solvent is sometimes called concentration, although usually concentration is expressed as a number of moles per unit volume.
Note that the ratio M/NA is the mass of a single atom or molecule in units of kg.
Related Sites for Number density
- Prediction of Density and Cetane Number of Diesel Fuel from GC … read Number density
- Density | Define Density at Dictionary.com read Number density
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