# Define drift velocity and derive an expression for it

Apoorva Arora IIT Roorkee
6 years ago
Thedrift velocityis the flowvelocitythat a particle, such as an electron, attains due to an electric field. It can also be referred to as axialdrift velocity. In general, an electron will propagate randomly in a conductor at the Fermivelocity.
Malavika Sajeev
12 Points
5 years ago
Dreift velocity is the velocity attained by any particle such as electron when kept in an electric field.
Derivation:
Consider a cross section of conductor with length ‘l’ and area ‘A’. Let n be the no of electrons per unit volume.
The volume of conductor can be given as
V = Al
No. of electrons=nAl
Charge, q = ne= neAl
When connected with a battery current I pass through it which is equal to,
I = $\frac{q}{t}$ =$\frac{neAl}{t}$    $\because l/t=V$d
we can write this equation as:
I= enAVd
Malavika Sajeev
12 Points
5 years ago
Consider a conductor of length ‘l’. When electric field is applied, each electron experiances a force,
F= -eE ($\because$direction of force is opposite to direction of electric field)
It has an acceleration, $a=\frac{F}{m}$
i.e $a = \frac{-eE}{m}$
we know $v = a\tau$
$\therefore$ Drift velocity, $Vd = -\frac{eE}{m}\tau$
k.divakar k.divakar
36 Points
4 years ago
The volume of the conductor =Avdt=area×distance
Charge in that volume=Avdtne. Since ne=q
Now,Avdtne=q
Avdne=q/t=I

Luckyraj Rathore
17 Points
4 years ago
the average velocity with which free electrons drift under the influence of an external field. Vd = -eE r/m
Deepak
15 Points
3 years ago
electrons move with an average velocity which is independent of time although electrons are accelerated this is the phenomenon of drift and velocity Vis called drift velocity
one year ago
Dear student,

The drift velocity is the flow velocity that a particle, such as an electron, attains due to an electric field. It can also be referred to as axial drift velocity. In general, an electron will propagate randomly in a conductor at the Fermi velocity.

Consider a conductor of length ‘l’. When electric field is applied, each electron experiances a force,
F = – eE ( F = qE, and q = – e)
Now, acceleration, a = F/m = – eE/m
Hence, v = u + aT = aT = – eE/m x T                      (assuming u = 0)
Hence, drift velocity, vd = – eET/m

Thanks and regards,
Kushagra