Define current density. Write an expression which connects current density with drift speed.

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Solution

Current density is defined as the ratio of current flowing in the conductor to the cross-sectional area of the conductor perpendicular to the direction of current flowing.
Relation between current density $J$ and drift speed $v_{d}$ is given by $J = n e v_{d}$
where $n$ is the number density of electrons and $e$ is the electronic charge.

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