Current Electricity

A wire of length 1 m has a resistance of $20 \Omega$ at $0^{\circ} \mathrm{C}$. It is uniformly stretched so that its length increases by $21 \%$. Assuming the volume of the wire remains constant, the percentage change in resistance is $n \%$. Alternatively, if the wire is heated [without stretching] through a temperature of $27^{\circ} \mathrm{C}$ and if the temperature coefficient of resistance of the material of wire is $0.004 K^{-1}$, the percentage change in resistance is $m \%$. The values of $m$ and $n$ are: