Q. Calculate the electric field in a copper wire of cross-sectional area 2 mm^{2} carrying a current of 1A . The resistivity of copper ρ = 1.7 x 10^{-8} ohm-m

(a) 8.5 mvm^{-1}

(b) 8 mvm^{-1}

(c) 9 mvm^{-1}

(d) 7 mv/m

Ans: (a)

Resistance $ \displaystyle R = \rho \frac{L}{A} $

$ \displaystyle L = \frac{R A}{\rho} $

Since V = IR and V = EL

$ \displaystyle E = \frac{V}{L} = \frac{I R}{L} $

$ \displaystyle E = \frac{I R}{\frac{R A}{\rho}} $

$ \displaystyle E = \frac{I \rho}{A} $