The number density of free electrons in a copper conductor is estimated to be $8.5 \times 10^{28} \ m^{-3}$. How long does an electron take to drift from one end of a wire $6 \ m$ long to its other end? The area of cross-section of the wire is $1.0 \times 10^{-6} \ m^2$ and it is carrying a current of $1.5 \ A$.

The electric field $E$,current density $J$ and conductivity $\sigma$ of a conductor are related as

What is relaxation time?

$(a)$ 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.

$A$ conducting wire of cross-sectional area $1 \,cm^2$ has $3 \times 10^{23}$ charge carriers per $m^3$. If the wire carries a current of $24 \,mA$, then the drift velocity of the carriers is:

At room temperature,copper has a free electron density of $8.4 \times 10^{28} \, m^{-3}$. The copper conductor has a cross-section of $10^{-6} \, m^2$ and carries a current of $5.4 \, A$. The electron drift velocity in copper is: