how current density, *j * = *nqv* _{ d }

explain this relation to me.

Hi Virender,

Let us consider a part of a conductor of cross-sectional area A, which is in the influence of an electric field as shown in the diagram below.

V

_{d}is the drift velocity, and Δt is the time taken by the electrons to cross the section. So the length of the taken part of the conductor is V_{d}Δt. The volume of this part of the conductor is AV_{d}Δt.Suppose n is the number of electrons per unit volume of the conductor. So, the number of electrons crossing the part of the conductor in time Δt is = n Х AV

_{d}Δt = nAV_{d}Δt. Hence, the net charge flowing through this part of the conductor in time Δt is,Q = (nAV

_{d}Δt) Х eIn the lesson the unit charge is taken as q, and here I’ve derived the equation using ‘e’ as the smallest charge.

So, we get a general equation, j = nqV

_{d}.Hope this helps you.

Keep posting and good luck!

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