Flow of Electric Charges in Metallic Conductors
In metallic conductors, electric current is due to the movement of free electrons, which move randomly in the absence of an electric field and drift in a specific direction when an electric field is applied.
What is Flow of Electric Charges in Metallic Conductors?
The average velocity attained by charge carriers (electrons in metals) in a conductor when an electric field is applied.
Key formula / rule: Current due to drift velocity
Key points
- Explain the mechanism of electric current flow in metals.
- Differentiate between random motion and drift velocity of electrons.
- Relate drift velocity to the electric field and conductor properties.
- Understand the direction of conventional current versus electron flow.
Common exam trap
Confusing random thermal motion with drift velocity.
Definitions
- Term
Drift Velocity (vd)
- Meaning
The average velocity attained by charge carriers (electrons in metals) in a conductor when an electric field is applied.
- Term
Relaxation Time (τ)
- Meaning
The average time interval between two successive collisions of an electron with the ions in the metallic lattice.
- Term
Current Density (J)
- Meaning
The electric current per unit cross-sectional area of a conductor.
Learning objectives
Explain the mechanism of electric current flow in metals.
Differentiate between random motion and drift velocity of electrons.
Relate drift velocity to the electric field and conductor properties.
Understand the direction of conventional current versus electron flow.
Formulae
- Name
Current due to drift velocity
- Note
n = number density of free electrons, A = cross-sectional area, vd = drift velocity, e = charge of electron
- Expression
I = nAved
- Name
Drift velocity
- Note
e = charge of electron, E = electric field, m = mass of electron, τ = average relaxation time
- Expression
vd = (eE/m)τ
- Name
Current density
- Note
J is current density
- Expression
J = I/A = nevd
- Name
Microscopic form of Ohm's Law
- Note
σ is conductivity, a material property
- Expression
J = σE
Prerequisites
Basic understanding of atomic structure and free electrons.
Concept of electric field and force on charges.
Common mistakes
Confusing random thermal motion with drift velocity.
Assuming electrons move in straight lines without collisions.
Incorrectly associating the direction of electron drift with the conventional current direction.
Keywords
Free electrons
Drift velocity
Electric field
Metallic conductor
Current density
Relaxation time
Ohm's Law (microscopic)
Practice preview
In metallic conductors, the electric current is due to the movement of:…
easy
The average time taken by a free electron to move between two successive collisions in a metallic conductor is called:…
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Which of the following statements about the drift velocity (v_d) of free electrons in a metallic conductor is INCORRECT?…
medium