The potential difference in open circuit for a cell is 2.2 volts. When a 4 ohm resistor is connected between its two electrodes the potential difference becomes 2 volts. The internal resistance of the cell will be

detailed solution

Correct option is D

The potential difference in open circuit for the cell is 2.2 volts, it means the emf of the battery should be 2.2 volts.Now a 4 ohm resistor is connected between its two electrodes, then the potential difference across the battery becomes 2 volts.V=ε−ir⇒2=2.2−ir⇒    ir=0.2  V                                                         ....iBut  i=εr+R=2.2r+4                              .....iiPutting the value of i in (i), we get r = 0.4 ohm.