For which of the following dependencies of drift velocity $v_d$ on electric field $E$ is Ohm's law obeyed?

There are $0.8 \times 10^{23}$ free electrons $/ cm^3$ in copper. If a $0.2 \, A$ current is flowing in a copper wire, then the drift velocity of electrons will be, given the cross-sectional area of the wire is $0.01 \, cm^2$.

An electric current flows along an insulated strip $PQ$ of a metallic conductor. The current density in the strip varies as shown in the graph. Which one of the following statements could explain this variation?

The drift velocity of an electron is $v_d$ in a conductor of area of cross-section $A$ and carries a current $I$. Now, the area of cross-section and current flowing through the conductor are doubled, then the new drift velocity of the electron is . . . . . . .

$A$ 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 $1.5 \times 10^{16}\,m^{-3}$.

If a current of $80 \ A$ is passing through a straight conductor of length $10 \ m$,then the total momentum of electrons in the conductor is (mass of electron $= 9.1 \times 10^{-31} \ kg$ and charge of electron $= 1.6 \times 10^{-19} \ C$).