Discuss the method of determination of unknown resistance by metre bridge method.

Explain drift of electrons and the origin of resistivity in conductors.
OR
Explain working of chemical cell. How emf is realised in a chemical cell and describe the relation between emf and internal resistance of the cell.

The equivalent resistance between the points $A$ and $B$ is

In the given circuit, total power consumed is $200 W.$ The value of resistance $R$ is

The resistance of the four arms $P, Q, R$ and $S$ in a Wheatstone's bridge are $2\mathrm{\Omega }, 4\mathrm{\Omega }, 4\mathrm{\Omega }$ and $8\mathrm{\Omega }$ respectively as shown in figure. Current through the galvanometer will be

The length $AB$ of slide wire bridge is $100 \mathrm{cm}$ long. Where should be free end of the galvanometer be connected on $AB$ so that galvanometer may show zero deflection?