$A$ 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.

What are called conductors and non-conductors? In which of these are free electrons more abundant: conductors or non-conductors?

The mechanism of the heat produced in a conductor when an electric current flows through it can be explained on the basis of

Which of the following is the unit of mobility of an electron in a conductor?

$(a)$ Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area $1.0 \times 10^{-7} \; m^{2}$ carrying a current of $1.5 \; A$. Assume that each copper atom contributes roughly one conduction electron. The density of copper is $9.0 \times 10^{3} \; kg/m^{3}$ and its atomic mass is $63.5 \; u$.
$(b)$ Compare the drift speed obtained above with,$(i)$ thermal speeds of copper atoms at ordinary temperatures,$(ii)$ speed of propagation of electric field along the conductor which causes the drift motion.

There is a current of $40 \ A$ in a wire of cross-sectional area $10^{-6} \ m^2$. If the number of free electrons per $m^3$ is $10^{29}$,then the drift velocity will be: