When there is an electric current through a conducting wire along its length,then an electric field must exist

$A$ silicon block at $300\,K$ has a length of $10\,cm$ and a cross-sectional area of $1 \times 10^{-4}\,m^2$. If a $2\,V$ battery is connected across its ends parallel to the length,find the current flowing through it. The electron mobility is $0.14\,m^2V^{-1}s^{-1}$ and the electron number density is $1.5 \times 10^{16}\,m^{-3}$.

Derive the equation of mobility in terms of relaxation time $(\tau)$. Write its unit.

$A$ constant potential difference is applied between the ends of a wire. If the length of the wire is elongated to $4$ times its original length,then the drift velocity of electrons will be:

$A$ 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

$A$ current of $10 \,A$ is maintained in a conductor of cross-section $1 \,cm^2$. If the number density of free electrons is $9 \times 10^{28} \,m^{-3}$,the drift velocity of free electrons is .......... $m/s$.