Explain with neat circuit diagram, how will you determine the unknown resistance by using a meter-bridge.

Describe how a potentiometer is used to compare the emfs of two cells by connecting the cells individually.

Two cells of emf $1.5 \mathrm{Volt}$ and $2 \mathrm{Volt}$ having respective internal resistances of $1\mathrm{\Omega }$ and $2\mathrm{\Omega }$ are connected in parallel so as to send current in same direction through an external resistance of $5\mathrm{\Omega }$. Find the current through the external resistance.