The reciprocal of resistance is

The resistance of a wire at $300 \, K$ is found to be $0.3 \, \Omega$. If the temperature coefficient of resistance of the wire is $1.5 \times 10^{-3} \, K^{-1}$, the temperature at which the resistance becomes $0.6 \, \Omega$ is: (in $K$)

$A$ wire of resistance $R$ is stretched until its radius is halved. What will be the new resistance (in $, R$)?

Equal potentials are applied on an iron and copper wire of the same length. In order to have the same current flow in the two wires, the ratio $r_{\text{iron}} / r_{\text{copper}}$ of their radii must be (Given that specific resistance of iron = $1.0 \times 10^{-7} \, \Omega \cdot \text{m}$ and specific resistance of copper = $1.7 \times 10^{-8} \, \Omega \cdot \text{m}$)

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

Constantan wire is used in making standard resistances because its