Two wires each of radius of cross section $r$ but of different materials are connected together end to end (in series). If the densities of charge carriers in the two wires are in the ratio $1 : 4$,the drift velocity of electrons in the two wires will be in the ratio:

The current density in a cylindrical wire of radius $r = 4.0 \, mm$ is $J = 1.0 \times 10^{6} \, A/m^{2}$. The current through the outer portion of the wire between radial distances $r/2$ and $r$ is $x \pi \, A$,where $x$ is ..........

Statement $(I)$: Specific resistance depends on the nature of the material and is independent of the temperature of the material.
Statement $(II)$: $A$ wire of resistance $6 \ \Omega$ is drawn out so that its new length is four times its original length. The resistance of the new wire is $48 \ \Omega$.
Statement $(III)$: Drift velocity is the average constant velocity acquired by free electrons inside a metal by the application of an electric field,which results in current.
Which of the following is correct?

$A$ copper wire of length $1\, m$ and radius $1\, mm$ is joined in series with an iron wire of length $2\, m$ and radius $3\, mm$ and a current is passed through the wires. The ratio of the current density in the copper and iron wires is

Two identical conductors are kept at the same temperature. If the ratio of the potential difference across them is $1 : 2$,what will be the ratio of their drift velocities?

The drift velocity of the electrons in a copper wire of length $2\ m$ under the application of a potential difference of $200\ V$ is $0.5\ m/s$. Their mobility (in $m^2 V^{-1} s^{-1}$) is