Which of the following graphs represents the variation of resistivity ( $\rho$ ) with temperature $(T)$ for copper?

Three copper wires of lengths and cross-sectional areas are $(l, A)$,$(2l, A/2)$,and $(l/2, 2A)$. Resistance is minimum in

Consider a thin square sheet of side $L$ and thickness $t$,made of a material of resistivity $\rho$. The resistance between two opposite faces,shown by the shaded areas in the figure is

Wires $A$ and $B$ have resistivities $\rho_A$ and $\rho_B$,where $\rho_B = 2 \rho_A$,and have lengths $l_A$ and $l_B$. If the diameter of wire $B$ is twice that of $A$ and the two wires have the same resistance,then the ratio $\frac{l_B}{l_A}$ is:

If the masses of three wires of same material are in the ratio of $1: 2: 3$ and their lengths are in the ratio of $3: 2: 1$,then electrical resistances of these wires are in the ratio

$A$ cylindrical metal wire of length $l$ and cross-sectional area $S$ has resistance $R$,conductance $G$,conductivity $\sigma$,and resistivity $\rho$. Which one of the following expressions for $\sigma$ is valid?