Which of the following materials is the best conductor of electricity?

$A$ uniform wire of length $l$ and radius $r$ has a resistance of $100\, \Omega$. It is recast into a wire of radius $\frac{r}{2}$. The resistance of the new wire will be ............... $\Omega$.

$A$ wire of resistance $2 R$ is stretched such that its length is doubled. Then the increase in its resistance is (in $R$)

The variations of resistivity $\rho$ with absolute temperature $T$ for three different materials $X, Y$ and $Z$ are shown in the graph below. Identify the materials $X, Y$ and $Z$.

Which of the following has a negative temperature coefficient of resistance?

How does the resistivity of a material depend on temperature? Write the empirical formula.