Calculate mean free path in $Cu$ at room temperature $300 \mathrm{K}\text{,}$ if number density of free electrons is $8.5\times {10}^{28} {\mathrm{m}}^{-3}$ and resistivity $\mathrm{\rho }=1.7\times {10}^{-8} \mathrm{ohm} \mathrm{m}$. Given $\mathrm{k}=1.38\times {10}^{-23} {\mathrm{m}}^2 \mathrm{kg} {\mathrm{s}}^{-2} {\mathrm{K}}^{-1}$.

A cell of emf $E$ is connected with an external resistance $R\text{,}$ then $\text{potential difference}$ across cell is $V$. The internal resistance of cell will be 

In the circuit shown, each resistance is $2 \mathrm{\Omega }$. The potential $V_1$, as indicated in the circuit, is equal to

A potentiometer is connected across $A$ and $B$ and a balance is obtained at $64.0 \mathrm{cm}$. When potentiometer lead to $B$ is moved to $C,$ a balance is found at $8.0 \mathrm{cm}$. If the potentiometer is now connected across $B$ and $C,$ a balance will be found at

A cell of emf $E$ having an internal resistance $r$ is connected to external resistance $R$. The potential difference $V$ across the resistance $R$ varies with $R$ as shown by the curve: