Discuss the variation of resistivity with temperature. Mention two important applications of the phenomenon.

Find the number of electrons that pass through a lamp in one hour if a steady current of $0.5 \mathrm{A}$ is maintained in it during the time.

A $12.5 \mathrm{V}$ battery operates a $14.2 \Omega$ flash light intermittently for a cumulative time of $65.3$minutes. Calculate the average current and the quantity of electricity furnished by the battery.

Find the number of free electrons in a copper wire of length $1\mathrm{m}$ and cross sectional area $1 {\mathrm{mm}}^2$. Determine the charge carried by these free electrons. Number density of free electrons in copper is $8.5\times {10}^{28}$ per ${\mathrm{m}}^3$.

A silver wire of cross section $1 {\mathrm{mm}}^2$ carries a current of $2\mathrm{A}$. Find the magnitude of current density in the wire.

Find the total charge carried by the number of free electrons in a copper wire of length $1 \mathrm{m}$ and cross section $1.6 {\mathrm{mm}}^2$ if density of copper is $9\times {10}^3 \mathrm{kg}/{\mathrm{m}}^3$ and its molecular mass is $63.5 {\mathrm{gmol}}^{-1}$. Assume valency of copper to be one.

A copper wire of radius $0.1 \mathrm{mm}$ and resistance $1 \mathrm{k\Omega }$ is connected across a power supply of $20 \mathrm{V}$. How many electrons are transferred per sec. between the supply and the wire at one end?

A copper wire of radius $0.1 \mathrm{mm}$ and resistance $1 \mathrm{k\Omega }$ is connected across a power supply of $20 \mathrm{V}$. Find the current density of the wire.

A wire of $2 \mathrm{mm}$ in diameter transfers a charge of $60 \mathrm{coul}.$ in $5 \mathrm{minutes}$. If the number density of electron in the wire is $5.8\times {10}^{28}$ per ${\mathrm{m}}^3$. Calculate the current in the wire.