Length of a conductor is increased by $1\%$. Calculate the percentage change in its resistance at constant volume.

Calculate resistance across $AB$ of the network shown in figure.

Two resistances $R_1$ and $R_2$ are connected in parallel. Derive the effective resistance of their parallel connection.
OR
Two cells of emf $E_1,E_2$ and internal resistance $r_1,r_2$ respectively are connected in series. Find the equivalent emf of their series connection.

Explain Wheat-stone bridge principle.

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