The drift velocity of electrons in a current-carrying wire of radius $r$ is $v$. If we want a drift velocity of $2v$ in a wire of the same material but with half the radius,what current must be passed through it?

An electric cell of emf $E$ is connected across a copper wire of diameter $d$ and length $l$. The drift velocity of electrons in the wire is $v_{d}$. If the length of the wire is changed to $2l$, the new drift velocity of electrons in the copper wire will be

$A$ copper wire of length $1 \,m$ and uniform cross-sectional area $5 \times 10^{-7} \,m^{2}$ carries a current of $1 \,A$. Assuming that there are $8 \times 10^{28}$ free electrons per $m^{3}$ in copper,how long will an electron take to drift from one end of the wire to the other?

$A$ 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,

Two wires $A$ and $B$ of the same material,having radii in the ratio $1: 2$,carry currents in the ratio $4: 1$. The ratio of drift speed of electrons in $A$ and $B$ is .......

The relaxation time in conductors