Usage
Using the number density as a function of spatial coordinates, the total number of objects N in the entire volume V can be calculated as
- ,
where
- is a volume element. If each object possesses the same mass m0, the total mass m of all the objects in the volume V can be expressed as
- .
Similar expressions are valid for electric charge or any other extensive quantity associated with countable objects. For example, replacing (total charge) 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 (and thus called molar concentration).
Read more about this topic: Number Density
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