Electric current is due to the drift of electrons in

Derive the equation of mobility in terms of electric current.

The quantities that do not change when a resistor connected to a battery is heated due to the current are:
$(A)$ drift speed
$(B)$ resistivity
$(C)$ resistance
$(D)$ number of free electrons

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

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 . . . . . . .

$A$ potential difference $V$ is applied across the ends of a metallic wire of length $l$. The drift velocity will be doubled if: