An electron takes $40\times {10}^3 \mathrm{s}$ to drift from one end of a metal wire of length $2 \mathrm{m}$ to its other end. The area of cross-section of the wire is $4 {\mathrm{mm}}^2$ and it is carrying a current of $1.6 \mathrm{A}$. The number density of free electrons in the metal wire is

Current density in a cylindrical wire of radius $R$ varies with radial distance as $\beta {\left(r+r_0\right)}^2$. The current through the section of the wire shown in the figure is.

Define current density. Write an expression which connects current density with drift speed.

Estimate the average drift velocity of the conduction electrons in a copper wire of cross section $2.0\times {10}^{-3}{\mathrm{cm}}^2$ carrying a current of 

$2.0 \mathrm{A}$ Assuming the density of conduction electrons to be $9\times {10}^{28}{\mathrm{m}}^{-3}$.

As following figure $2 \mathrm{A}$ current passing through a conducting wire, radius of cross sectional of wire at point $A$ is $3r$ and point $B$ is $r$ respectively. Then find the ratio of drift velocity at point $A$ & $B$.

A. The drift velocity of electrons decreases with the increase in the temperature of conductor.
B. The drift velocity is inversely proportional to the area of cross-section of given conductor.
C. The drift velocity does not depend on the applied potential difference to the conductor.
D. The drift velocity of electron is inversely proportional to the length of the conductor.
E. The drift velocity increases with the increase in the temperature of conductor.

Choose the correct answer from the options given below:

A uniform copper wire having a cross-sectional area of $1 {\mathrm{mm}}^2$ carries a current of $5 \mathrm{A}$. Calculate the drift speed of free electrons in it. (Free-electron number density of copper$=2\times {10}^{28}/{\mathrm{m}}^3$)