When the terminals of a cell are connected to a conductor of resistance R, an electric…

When the terminals of a cell are connected to a conductor of resistance R, an electric current flows through the circuit. The electrolyte of the cell also offers some resistance in the path of the current, like the conductor. This resistance offered by the electrolyte is called internal resistance of the cell (r). It depends upon the nature of the electrolyte, the area of the electrodes immersed in the electrolyte and the temperature. Due to internal resistance, a part of the energy supplied by the cell is wasted in the form of heat.
When no current is drawn from the cell, the potential difference between the two electrodes in known as emf of the cell ( \(\varepsilon\) ). With a current drawn from the cell, the potential difference between the two electrodes is termed as terminal potential difference (V).

Potential difference across a cell in the open circuit is 6 V. It becomes 4 V when a current of 2 A is drawn from it. The internal resistance of the cell is: