$A$ beam contains $2 \times 10^8$ doubly charged positive ions per cubic centimeter,all of which are moving with a speed of $10^5 \,m/s$. The current density is ............. $A/m^2$.

$A$. The drift velocity of electrons decreases with the increase in the temperature of a conductor.
$B$. The drift velocity is inversely proportional to the area of cross-section of a given conductor.
$C$. The drift velocity does not depend on the applied potential difference to the conductor.
$D$. The drift velocity of an electron is inversely proportional to the length of the conductor.
$E$. The drift velocity increases with the increase in the temperature of a conductor.
Choose the correct answer from the options given below:

$A$ metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases,the drift velocity of the electron in it

The drift velocity of free electrons in a conductor is $v$ when a current $i$ is flowing in it. If both the radius and current are doubled,then the drift velocity will be

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:

When current flows through a conductor,the order of magnitude of the drift velocity of electrons is