The $SI$ unit of the current density is . . . . . . .

$A$ metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases,the drift velocity of the electron in it

In the given figure,a battery of emf $E$ is connected across a conductor $PQ$ of length $L$ and different area of cross-sections having radii $r_{1}$ and $r_{2}$ $(r_{2} < r_{1})$. Choose the correct option as one moves from $P$ to $Q$:

The electric intensity $E$,current density $j$,and specific resistance $\rho$ (often denoted as $k$ in some texts) are related to each other by the relation:

$A$ copper wire of length $1 \ m$ and radius $1 \ mm$ is connected in series with an iron wire of length $2 \ m$ and radius $3 \ mm$. If a current flows through both wires,the ratio of the current density in the copper wire to that in the iron wire will be:

The relaxation time in conductors