## Current Density in a Conducting Medium

Currents in metals are due to the movement of charge carriers ‘electrons’.

where

as current per unit area has the advantage, since the dimensions of the

conducting medium are not directly involved. Relation between current

density and charge density

*I*is the current in Amperes and*A*is the cross-sectional area of conducting medium in metre^{2}. Describing current density*J*as current per unit area has the advantage, since the dimensions of the

conducting medium are not directly involved. Relation between current

density and charge density

*ρ*is described in the following:**Current density:**Current

*I*(Amperes) through a conductor by definition is

*Charge*(in Coulombs)/

*Time*

(in seconds). Current is due to the movement of charges through a

conducting medium in a given time. If, 1 C of charge moves through a

conducting medium in 1 s, the resulting

*current*is 1 A.

electrons carry 1 Coulomb of charge. So the movement of 6.25 × 10

^{18}electrons for 1 s contributes to 1 A of current in a conductor.where

*q*is the charge of an electron and*N*is the number of electrons in a given volume. If the charge passes through a distance*L*(metres) in time*T*(seconds), through a conducting medium, then the velocity*v*with which the electrons move is*L*/*T*.Substituting the value of

*T*from Eq. (2.13) in Eq. (2.12), we getwhere

*n*=*N*/*AL*is the concentration of electrons that is the number of electrons per unit volume.Using

*v*=*μE*in Eq. (2.16), we getwhere

*μ*is the mobility of charge carriers.Current density

*J*_{p}due to the movement of Holes =*pqμ*_{p}*E.*
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