CBSE 2024 · Region 2 · Set 3 · Q17 · 2 marks
An electric field E is maintained in a wire of length ' $\displaystyle l$ ' and area of cross-section 'a'. Derive the relation between the current density ' $\displaystyle \sigma$ ' in the wire and the electric field E .
Marking-scheme solution
$\displaystyle V=I R$
$\displaystyle E l=\frac{I \rho l}{A}$ ($\displaystyle V=E l$, $\displaystyle R=\frac{\rho l}{A}$)
$\displaystyle E=\rho \frac{I}{A}$
$\displaystyle E=\sigma \rho$
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