Physical Significance of Displacement Current
Discusses that displacement current, though not a flow of charges, acts as a source of magnetic field, similar to conduction current, due to changing electric fields.
What is Physical Significance of Displacement Current?
A current that is associated with a time-varying electric field, defined as the product of the permittivity of free space and the rate of change of the electric field through a surface.
Key formula / rule: Displacement Current
Key points
- Understand the origin and nature of displacement current.
- Differentiate between conduction current and displacement current.
- Appreciate the role of displacement current in Maxwell's equations.
- Explain the significance of displacement current in electromagnetic wave propagation.
Common exam trap
Confusing displacement current with conduction current.
Definitions
- Term
Displacement Current
- Meaning
A current that is associated with a time-varying electric field, defined as the product of the permittivity of free space and the rate of change of the electric field through a surface.
- Term
Conduction Current
- Meaning
A current that arises from the actual flow of charge carriers, such as electrons or ions, through a conductor.
- Term
Electric Flux
- Meaning
A measure of the electric field passing through a given surface area, calculated as the surface integral of the electric field vector over the area.
Learning objectives
Understand the origin and nature of displacement current.
Differentiate between conduction current and displacement current.
Appreciate the role of displacement current in Maxwell's equations.
Explain the significance of displacement current in electromagnetic wave propagation.
Formulae
- Name
Displacement Current
- Note
Where ε₀ is the permittivity of free space and dΦE/dt is the rate of change of electric flux.
- Expression
Id = ε₀ dΦE/dt
- Name
Displacement Current Density
- Note
Where Jd is the displacement current density and dE/dt is the rate of change of electric field.
- Expression
Jd = ε₀ dE/dt
- Name
Ampere-Maxwell Law
- Note
Relates the line integral of the magnetic field around a closed loop to the total current (conduction current Ic + displacement current Id) passing through the surface bounded by the loop.
- Expression
∮ B⋅dl = μ₀(Ic + Id)
Prerequisites
Electric Flux
Gauss's Law for Electricity
Ampere's Law
Capacitors
Electromagnetic Induction
Common mistakes
Confusing displacement current with conduction current.
Forgetting that displacement current is related to the *change* in electric flux, not the flux itself.
Assuming displacement current requires a medium.
Keywords
Displacement Current
Electric Flux
Changing Electric Field
Magnetic Field
Maxwell's Equations
Ampere's Law
Electromagnetic Waves
Capacitor
Practice preview
In a parallel plate capacitor being charged, where is the displacement current significant?…
medium
Which of the following best describes the physical significance of displacement current?…
easy
The Ampere-Maxwell law in its integral form is given by ∮ B ⋅ dl = μ₀(Ic + I_d), where I_d is the displacement current. What is the primary role of the displacement current term in this equation?…
medium