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Current Density (J)

Current density at any point inside a conductor is defined as a vector having magnitude equal to current per unit area surrounding that point. Remember area is normal to the direction of charge flow (or current passes) through that point.
  • Current density at point P is given by 70268.png
    Fig. 3
  • If the cross-sectional area is not normal to the current, but makes an angle θ with the direction of currentm then
    di = JdA cos θ 70280.png
  • If current density 70286.png is uniform for a normal cross-section 70292.png, then J = i/A.
  • Current density 70307.png is a vector quantity. Its direction is same as that of 70313.png. Its SI unit is amp/m2 and dimension [L–2A].
  • In case of uniform flow of charge through a cross-section normal to it as i = nqvA J = i/A = nqv.
    Fig. 4
  • Current density relates with electric field as 70328.png, where σ = conductivity, and ρ = resistivity or specific resistance of substance.

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