Question

derive relation between electric current and drift velocity

Answer 1

q = n a l e

where n is number density(N / V)...........a is area...............l is length...& V = a l ........e is elementry charge

time = dist / speed . .................. so t = l / vd

I = q / t

I = n a e vd

Answer 2

Answer:

Allow us to consider a conductor of cross sectional area A. The volume element for a length Δx is AΔx.  

If n is the number of electrons according to unit volume, the number of electrons in this volume element can be n*AΔx.  The overall charge in this volume element is Δq=n*AΔx*e, in which e is charge on the electron.  

If electrons drift with a velocity vd because of thermal strength, the space traveled in time Δt is Δx=vd*Δt.  

On substituting this value of Δx within the expression for Δq, we discover that total charge within the volume element below consideration is given by means of;

Δq=n*A*e*vd*Δt  

After modification;

Current I= Δq/Δt= n*A*e*vd