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What is Drift Velocity? Know it's Definition, Formula & Related Concepts
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Current Electricity
As the JEE Main Exam 2020 notification is out, so we should cover the most important topics. We are here with one of the most important topics of Physics. We will study: what is drift velocity in physics, what is the drift velocity of an electron, and will explore the relation between drift velocity and current?
What is Drift Velocity?
To know what this term is, we should first know the meaning of drift. Drift means a slow movement towards something so the topic is all about movement.
Now the question arises what do you mean by drift velocity? The answer is: It is the average velocity attained by charged particles in a material due to the influence of an electric field.
Drift velocity is proportional to current. In a resistive material, it is also proportional to the magnitude of an external electric field. Therefore, Ohm’s law can be explained as:
u = μE
where u is drift velocity, μ is the electron mobility of electron, and E is the electric field. These quantities’ units are m/s, m2/(V·s), and V/m, respectively.
What is Drift Velocity of an Electron?
The free electrons move in a conductor with random velocities in random directions. When we apply an electric field across the conductor, the randomly moving electrons experience an electrical force in the direction of the field.
Due to this field, the electrons continue their randomness of motion, but they will shift towards higher potential with their random motion. That means the electrons will drift towards the higher potential end of the conductor along with their random motions. Thus, every electron will have a net velocity towards the end of the conductor with higher potential and we refer to this net velocity as the drift velocity of electrons. The current due to this drift movement of electrons inside a conductor is known as drift current.
The average velocity gained by the free electrons of a conductor, with which the electrons get drifted under the influence of electric field is given by
v = I/nAq
Where v is the drift velocity of electrons.
‘I’ is the current flowing through the conductor measured in Amperes.
A is the area of cross-section of the conductor measured in m2.
q is the charge on an electron measured in Coulombs.
n is the no. of electrons.
Relation between Drift Velocity and Current
Let l is the length of the conductor and A is the area of cross-section.
Therefore, the volume of the conductor = Al
If n is the number of free electrons per unit volume of the conductor, then the total number of free electrons in the conductor=A/n.
If e is the charge on each electron then the total charge on all the free electrons of the conductor
Q=A/ne………….(1)
Let a constant potential difference V is applied across the ends of the conductor
The electric field across the conductor is given by
E=V/l
Due to this field, the free electrons in the conductor will begin to move towards the left-hand side of the conductor with a drift velocity vd.
Thus the time taken by the free electrons to cross the conductor is
t=l/vd………………..(2)
As current I=q/t………….(3)
By substituting equations (1) and (2) in equation (3),
We get
I=Alne/l/vd
Or I=Anevd……………..(4)
Since A,n and e are constant
I∞vd
Hence the current flowing through a conductor is directly proportional to the drift velocity of electrons inside it.
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Important Notes - Electrons in a conductor shift towards the high potential end of the conductor when we apply an electric field across it.
- The current flowing in a conductor is directly proportional to the drift velocity of electrons.
- The electrons inside a conductor move with random velocities in random directions unless an electric field is applied to the conductor.
Hope that the article was helpful to define what is drift velocity and all the important concepts about it. Get some practice of the same on our free Testbook App. Download Now!
Drift Velocity FAQs
What is Drift Velocity?
Drift velocity is the average velocity of charge carriers, such as electrons or holes, in a conductor when an electric field is applied.
How is Drift Velocity related to Current?
Drift velocity is directly proportional to the current flowing in the conductor.
What factors affect the Drift Velocity of charge carriers?
The Drift Velocity of charge carriers is affected by factors such as the strength of the electric field, the density of charge carriers, and the mobility of charge carriers.
What is the significance of Drift Velocity in electronics?
Drift velocity is an important parameter in the design and analysis of electronic devices such as transistors, where the flow of charge carriers is controlled by an applied electric field.
How can Drift Velocity be measured?
Drift velocity can be measured indirectly by measuring the resistance of a conductor and the current flowing through it, or directly by using specialized instruments such as a Hall effect sensor.