At what temperature will the resistance of a copper wire become three times its value at $0^{\circ}C$? (Temperature coefficient of resistance for copper = $4 \times 10^{-3} \,^{\circ}C^{-1}$)

Two wires of equal length,one of aluminium and the other of copper,have the same resistance. Which of the two wires is lighter? Hence,explain why aluminium wires are preferred for overhead power cables. $(\rho_{Al} = 2.63 \times 10^{-8} \; \Omega m, \rho_{Cu} = 1.72 \times 10^{-8} \; \Omega m, \text{Relative density of } Al = 2.7, \text{of } Cu = 8.9.)$

$A$ material '$B$' has twice the specific resistance of '$A$'. $A$ circular wire made of '$B$' has twice the diameter of a wire made of '$A$'. Then,for the two wires to have the same resistance,the ratio $\frac{l_B}{l_A}$ of their respective lengths must be

$A$ wire of resistance $x \ \Omega$ is drawn out,so that its length is increased to twice its original length,and its new resistance becomes $20 \ \Omega$. Then $x$ will be ........ $\Omega$.

$A$ cylindrical metallic wire is stretched to increase its length in such a way that the metallic wire changes its resistance by $6\%$. The percentage increase in its length is (in $\%$)

$A$ copper wire is stretched to increase its length by $0.1\%$. What is the percentage increase in the resistance of the wire (in $\%$)?