Kirchhoff 's junction rule is a reflection of

The variation of terminal potential difference $$V$$ with current flowing through a cell is as shown. The emf and internal resistance of the cell are

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