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How does the number of charge carriers per unit volume affect electric current?

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density current: descent to the ocean floor — density current Diagram showing the behaviour of a density current as it descends to the seafloor.

The number of charge carriers per unit volume is a fundamental factor in determining the magnitude of an electric current.

In physics, the current $i$ flowing through a conductor is directly related to the density of these carriers. Specifically, if there are $n$ free particles of charge $q$ per unit volume moving with an average velocity $v$ through a cross-sectional area $A$ , the current is determined by the collective flow of these charges. Because current is defined as the amount of charge crossing a plane per unit of time, increasing the concentration of available charge carriers ( $n$ ) increases the total charge available to flow through the conductor, thereby increasing the current for a given velocity and area.12

The overall electrical conductivity of a material is dependent on both this carrier concentration and the mobility of the carriers—the rate at which they move under the influence of an electric field. In materials like semiconductors, for example, the number of carriers can be intentionally increased through a process called doping to enhance conductivity.2