The reciprocal of resistance is

Two conductors are made of the same material and have the same length. Conductor $A$ is a solid wire of diameter $1.0 \, mm$. Conductor $B$ is a hollow tube of outside diameter $2.0 \, mm$ and inside diameter $1.0 \, mm$. The resistance ratio $R_A/R_B$ will be

At what temperature $(^oC)$ will the resistance of a copper wire become three times its value at $0^oC$? (Given: Temperature coefficient of resistance of copper at $0^oC$ is $\alpha = 4 \times 10^{-3} / ^oC$)

The cross-sections of wires made of the same material and having the same length are shown in the figure. What can be said about their resistances?

$A$ wire of resistance $R$ and radius $r$ is stretched until its radius becomes $r / 2$. If the new resistance of the stretched wire is $x R$,then the value of $x$ is $\qquad$

$A$ conducting wire has length $L_1$ and diameter $d_1$. After stretching,the same wire's length becomes $L_2$ and diameter $d_2$. The ratio of resistance before and after stretching is: