$A$ wire of non-uniform cross-section is carrying a steady current. Along the wire,

$A$ conductor of length $1.5 \ m$ and area of cross-section $3 \times 10^{-5} \ m^2$ has an electrical resistance of $15 \ \Omega$. The current density in the conductor for an electric field of $21 \ Vm^{-1}$ is

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

$A$ current of $1.344 \, A$ flows through a copper wire of cross-sectional area $1 \, mm^2$. If the number of free electrons per unit volume is $8.4 \times 10^{22} \, cm^{-3}$,then the drift velocity is:

Define mobility and write its $SI$ unit.

An ionization chamber with parallel conducting plates as anode and cathode has $5 \times 10^7$ electrons and the same number of singly-charged positive ions per $cm^3$. The electrons are moving at $0.4\, m/s$. The current density from anode to cathode is $4\,\mu A/m^2$. The velocity of positive ions moving towards cathode is ............. $m/s$. [$AIPMT$ $1992$]