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Chapter 27 - 27.23

23. We use J = E/ρ ,where E is the magnitude of the (uniform) electric ﬁeld in the wire, J is the magnitude

of the current density, and ρ is the resistivity of the material. The electric ﬁeld is given by E = V/L ,

where V is the potential diﬀerence along the wire and L is the length of the wire. Thus J = V/Lρ and

ρ = V

115V

(10m) 1 . 4

10 4 A / m 2 =8 . 2

10 − 4 Ω

m .

LJ =