A cell of constant e.m.f. first connected to a resistance \[{{R}_{1}}\] and then connected to a resistance \[{{R}_{2}}\]. If power delivered in both cases is then the internal resistance of the cell is [Orissa JEE 2005]

• A.            \[\sqrt{{{R}_{1}}{{R}_{2}}}\]
• B.                                      \[\sqrt{\frac{{{R}_{1}}}{{{R}_{2}}}}\]
• C.            \[\frac{{{R}_{1}}-{{R}_{2}}}{2}\]                                       
• D.            \[\frac{{{R}_{1}}+{{R}_{2}}}{2}\]