A cell develops the same power across two resistance `R_(1)` and `R_(2)` separately. The internal resistance of the cell is

Explanation

Let r be the internal resistance of the cell and E its EMF. When connected across the resistance `R_(1)` in the circuit, current passing through the resistance is
`i=(E)/(R_(1)+r)" "therefore" "P_(1)=i^(2)R_(1)=((E)/(R_(1)+rr))^(2)R_(1)`
Similarly `P_(2)-((E)/(R_(2)+r))^(2)R_(2)" Given that "P_(1)=P_(2)`
Substituting the values, we get `r=sqrt(R_(1)R_(2))`