Physics - Current Electricity Question with Solution | TestHub

Volume of wire having cross-sectional area $A$ and length $l$ is, $V=\text{A}l$

Resistance of a wire is given by, $R=\frac{\rho l}{A}=\frac{\rho l}{\frac{V}{l}}=\frac{\rho l^2}{V}$As change in length is small,

$\frac{\Delta R}{R}\times 100\%=\frac{2\Delta l}{l}\times 100\%=2\times 0.4\%=0.8\%$