$A$ charged particle is moving in an electric field of $3 \times 10^{-10} \text{ Vm}^{-1}$ with mobility $2.5 \times 10^6 \text{ m}^2 \text{V}^{-1} \text{s}^{-1}$. Its drift velocity is:

$A$ cylindrical resistor is connected across a battery $\varepsilon$. The cylinder has a uniform free electron density, and the middle part of the cylinder has a larger radius as shown in the figure. Which of the following graphs represents the variation of $V_d$ (drift velocity) with respect to $x$ (distance along the length of the resistor)?

$A$ current of $1.6\, A$ is flowing through a wire having a cross-sectional area of $1\, mm^2$. If the density of free electrons in the material of the wire is $10^{29}\, m^{-3}$,the drift velocity of the electrons will be:

$A$ steady current $I$ is set up in a wire whose cross-sectional area decreases in the direction of the flow of the current. Then,as we examine the narrowing region,

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

Write Ohm's law in the form of current density (vector form).