The number density of free electrons in copper is nearly $8 \times 10^{28} \ m^{-3}$. $A$ copper wire has an area of cross-section $= 2 \times 10^{-6} \ m^2$ and is carrying a current of $3.2 \ A$. The drift speed of the electrons is $..... \times 10^{-6} \ m \ s^{-1}$.

$A$ 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,

Assume a hypothetical wire in which free electron density changes with temperature in proportionality $n \propto T$,assuming $\tau$ (relaxation time of collision) and dimensions of the wire remain unchanged with increasing temperature. Which one of the resistance $v/s$ temperature graphs is true?

$A$ wire has a non-uniform cross-section as shown in the figure. $A$ steady current flows through it. The drift speed of electrons at points $P$ and $Q$ is $v_P$ and $v_Q$ respectively.

$A$ 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:

Derive the relation between electric current and drift velocity.