The pace and direction of motion are measured using a vector. In simpler words, velocity refers to the rate at which something goes in one direction. Velocity might be used for computation of the speed of a car travelling north on a major highway and the speed of a rocket launching into space. Velocity of drift of the missing quantity can be easily calculated using the drift velocity formula if any three of the four parameters are known. Let us now take a closer look into drift velocity in this article.

What is Drift Velocity?

To comprehend this concept, we must first comprehend drift. Drift is defined as the slow movement of an object toward something. 

According to the notion of drift velocity, subatomic particles, such as electrons drift in random directions. When electrons are exposed to an electric field, they shift randomly. Although, they drift steadily in one direction within the applied electric field’s direction. 

The drift velocity is also known as the net velocity at which electrons will drift. The SI unit for drift velocity is meters per second (m/s) or meters per square meter.

Drift velocity formula

The electrons which move down a conductor at a rate, and hence the pace at which charge flows, or current, is measured by the velocity of drift. As a result, the ohmic resistance is proportional to velocity of drift.

Drift velocity is proportional to the force and the magnitude of the external electric field in a resistive material. The formula of drift velocity can be stated as follows using ohm’s law:

u= μE

In the equation mentioned above,

The drift velocity is denoted by the letter = u

Electron mobility (the movement of electrons) =

The electric field is noted by  E

Another drift velocity formula is as follows:

• This can also be noted as the electric current and drift velocity relationship.
• I=nAvQ
• The current flowing through the conductor is measured in amperes and is denoted by I
• The number of electrons within any molecule = n
• The conductor’s cross-sectional area is represented as = A
• The electrons’ drift velocity = v
• The charge of an electron, measured in Coulombs = Q

Current Density and Drift Velocity Relationship

The total current flowing through a cross-sectional conductor unit in a unit of time is known as the current density. The formula for drift velocity is well-known.

V=1nAq

I=nAvQ

J=IA=nVQ

Here,

• The current density measured in Amperes per square meter = J
• The electron’s drift velocity is denoted by the letter ‘v.’

As a result, we can deduce that the electron’s velocity and current density are similar. Furthermore, when the intensity of the electric field increases, the velocity of the electric field increases, and the flow of current through the conductor increases.

Derivation of velocity of drift

F= -μE

a= FM

a= -μEm

=v+at

Therefore now,  let us consider v = 0

Then, t = T

T is Relaxation time 

“Relaxation time” is the time between two successive collisions of electrons with positive ions in the metallic lattice.

Relaxation time formula (T) = (T1+T2+…Tn)/n

Hence, T is also called τ, which is the mean free path/velocity of electrons (root mean square)

T = = v r.m.s

Getting back to the previous equation 

u=v+at

u=aT                           (After substituting for v & u)

u= -μEmT

This is the outcome of the derivation.

Points to remember

• The average velocity obtained by particles such as electrons under the influence of an electric field is known as drift velocity.
• Drift velocity is measured in millimetres per second (m/s). It’s usually measured in square meters per square meter.
• An electron’s drift velocity is relatively low, usually in the range of 10-3ms-1.
• Because the electron’s movement speed is known as drift velocity, the current formed by the drift movement of electrons in an electrically charged conductor is the drift current.
• The drift velocity formula for calculation is I=nAvQ.

Conclusion

When an electric field is applied across a conductor, the electrons are drawn to the wire’s high potential end. The electric current flowing within the conductor is proportional to the electron’s drift velocity. The electrons inside the conductor move at random velocities and in random directions unless an electric field is applied. Current is directly proportional to drift Velocity, but r2 is inversely proportional. Drift velocity formula can be used  for calculating different velocities.