Potentiometer Questions

In a potentiometer experiment the balancing with a cell is at length $240\text{ cm}$. On shunting the cell with a resistance of $2\Omega$ the balancing length becomes $120\text{ cm}$. The internal resistance of the cell is:

The length of a wire of a potentiometer is $100\text{cm}$, and the e.m.f. of its standard cell is $E$ volt. It is employed to measure the e.m.f. of a battery whose internal resistance is $0.5\Omega$. If the balance point is obtained at $l=30\text{cm}$ from the positive end, the e.m.f. of the battery is: