Question

Write short notes on conduction and convection current density.

Answer 1

Conduction current is something you would witness in a conducting material, such as a metal. It refers to the movement of current in the presence of an electric field and can be described by Ohm's law. Convection current is current flow in an insulating medium. This, however, does not follow Ohm's law. We can define current as the electric charge passing through an area per unit volume. I = d Q d t I=dQdt per unit time. Current density is the amount of current flowing through a surface per unit time J = Δ I Δ S J=ΔIΔS with I = ∫ J ⋅ d S I=∫J⋅dS. In a convection current, we have a current flowing through an insulating medium Δ I = Δ Q Δ t = ρ Δ S Δ y Δ t = ρ Δ S u y ΔI=ΔQΔt=ρΔSΔyΔt=ρΔSuy where S is the surface the current is passing through, y is the length along the velocity vector, and u y uy is the velocity vector. So we can express the convection current as J y = Δ I Δ S = ρ ⋅ u y Jy=ΔIΔS=ρ⋅uy. Conduction current density will describe the ability for an electric field E to propagate through a medium, controlled by the proportionality constant sigma, or conductivity. So, both describe a "current", but it might be easier to replace the word "current" with "flow; convection describes the flow through an insulating medium, and conductivity describes flow through a conducting medium.

Reference https://www.physicsforums.com/threads/difference-between-conduction-convection-current-density.926676/

Answer 2

Conduction current is observed in a conductive material, like metal. It is the current movement in the presence of an electric field, and can be defined in the law of Ohm, whereas current convection is natural movement in an insulating medium.

• Convention Current density is a relationship between the current density and the volumetric charge density speed at a given point. Simply put, is the sum of current that passes through a surface S in a time t. This surface is continuously perpendicular to current flow.
• Conduction Current Density is the amount of current flowing in a time t on a conductor's surface. The surface is always parallel to flowing current and gives a material its conductive nature, because the energy gap between the material's valence band and its conductive band is narrow