Difference between Conduction Current and Displacement Current

Conduction current is the movement of electric charge through a conducting material, like a wire. Displacement current is a concept in electromagnetism, which represents changing electric fields in non-conductive materials. In this article, we will learn the differences between Conduction Current and Displacement Current in detail.

What is Conduction Current?

Conduction current refers to the flow of electric charge through a conducting material, such as a metal wire or an electrolyte solution. It occurs when free electrons move in response to an electric field applied across the conductor. This movement of charge constitutes an electric current.

• Conduction current originates from the movement of free electrons within the conductor.
• It flows in the direction opposite to the flow of electrons.
• The magnitude of conduction current depends on the number of free electrons and their drift velocity.
• Conduction current increases with an increase in applied voltage and decreases with a decrease in voltage.
• It occurs only in materials with free charge carriers, such as metals and ionized solutions.
• Conduction current can be affected by temperature changes, with higher temperatures generally resulting in greater conductivity and current flow.
• The magnitude of conduction current (I) is given by Ohm’s Law:

I =V​ /R

where V is the applied voltage and R is the resistance of the conductor.

What is Displacement Current?

Displacement Current is a physical quantity related to Maxwell’s equation that has the property of the electric current. It is defined as the rate of change of the electric displacement field (D).

• Displacement current does not appear from the actual movement of the electric charge as in the case of the conduction current but is produced by time changing electric field.
• It is a vector quantity.
• Electromagnetic waves propagate with the help of displacement current.
• A charging capacitor has no conduction of charge but the charge accumulation in the capacitor changes the electric field link with the capacitor that in turn produces the current called the Displacement Current. This current is given by,

I_D = J_DS = S(∂D/∂t)

where,

• S is the area of the Capacitor Plate
• I_D is the Displacement Current
• J_D  is the Displacement Current Density.
• D is related to Electric Field E as, D = εE
• ε is the Permittivity of material between plates

Maxwell’s Equation defines the displacement current which has the same unit as the electric current, the Maxwell field equation is represented as, 

∇×H = J + J_D

where,

• H is related to magnetic field B as B = μH
• μ is the permeability of the material between the plates
• J is the Conducting Current Density.
• J_D  is the Displacement Current Density.

Difference between Conduction Current and Displacement Current

Here is a comparison of the differences between conduction current and displacement current:

Aspect	Conduction Current	Displacement Current
Definition	Conduction current is the flow of charge through a conductor.	Displacement current is a concept used in Maxwell’s equations to describe a changing electric field in a dielectric (non-conducting) medium.
Nature of Flow	Involves the actual movement of free charge carriers like electrons.	Does not involve actual charge movement; related to the rate of change of electric displacement field.
Associated Materials	Occurs in conductive materials.	Occurs in both conductive and non-conductive materials, including vacuum.
Required Conditions	Requires a physical medium with free charge carriers.	Requires a changing electric field, irrespective of the presence of a medium.
Mathematical Expression	Given by I = nqAv, where n is charge density, q is charge, A is area, and v is drift velocity.	Given by ID​ = ϵ0​d(ΦE)/dt​​, where ϵ0​ is permittivity of free space and ΦE​ is electric flux.
Magnetic Field	Produces a magnetic field according to Ampere’s Law.	Included in Ampere’s Law with Maxwell’s addition to explain magnetic fields where no real charges flow.
Role in Circuits	Primarily considered in electrical circuits.	Important in understanding electromagnetic waves and capacitors in AC circuits.

FAQs on Conduction and Displacement Current

What is conduction current?

Conduction current is the flow of electrical charge through a conductor, like a wire, facilitated by the movement of electrons or other charge carriers.

What is displacement current?

Displacement current doesn’t involve actual charge movement but represents a changing electric field in a dielectric or vacuum, crucial for maintaining continuity in Maxwell’s equations.

How are conduction current and displacement current related to Maxwell’s equations?

Conduction current is part of the original Ampere’s Law, while displacement current was Maxwell’s addition to this law, helping to describe magnetic fields in regions without free charge flow.

Where does displacement current occur?

Displacement current can occur in both conductive and non-conductive materials, including vacuums, wherever there is a time-varying electric field.

Can displacement current generate a magnetic field?

Yes, displacement current generates a magnetic field similar to conduction current, as predicted by Maxwell’s addition to Ampere’s Law.

Why is displacement current important in capacitors?

In capacitors, displacement current allows magnetic fields to exist across the gaps where no real charge flows, facilitating AC circuit analysis.