The resistance of a coil is $4.2\, \Omega$ at $100\,^{\circ}C$ and the temperature coefficient of resistance of its material is $0.004\,^{\circ}C^{-1}$. Its resistance at $0\,^{\circ}C$ is ............. $\Omega$.

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

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 resistance of a wire is $R \; \Omega$. If it is melted and stretched to $n$ times its original length,its new resistance will be

$A$ conducting wire of length $l$,area of cross-section $A$,and electric resistivity $\rho$ is connected between the terminals of a battery. $A$ potential difference $V$ is developed between its ends,causing an electric current. If the length of the wire of the same material is doubled and the area of cross-section is halved,the resultant current would be:

Arrange the following materials in increasing order of their resistivity: Nichrome,Copper,Germanium,Silicon.