There are two wires of the same length and of the same material and radii $r$ and $2r$. The ratio of their specific resistance is

Two wires of same length and thickness having specific resistances $6 \, \Omega \, cm$ and $3 \, \Omega \, cm$ respectively are connected in parallel. The effective resistivity is $\rho \, \Omega \, cm$. The value of $\rho$ to the nearest integer is ..... .

Masses of three wires of copper are in the ratio of $1: 3: 5$ and their lengths are in the ratio of $5: 3: 1$. The ratio of their electrical resistances is

If a wire is stretched to make it $0.1 \%$ longer,its resistance will

$A$ wire $100\,cm$ long and $2.0\,mm$ diameter has a resistance of $0.7\,\Omega$. The electrical resistivity of the material is ...........$ \times 10^{-6}\,\Omega \cdot m$.

Why does the resistance of metallic conductors and semiconductors change differently with a change in temperature?