Two sources of equal $emf$ are connected to an external resistance $R$. The internal resistances of the two sources are ${R_1}$ and ${R_2}\,({R_2} > {R_1})$. If the potential difference across the source having internal resistance ${R_2}$ is zero, then
  • A$R = {R_1}{R_2}/({R_1} + {R_2})$
  • B$R = {R_1}{R_2}/({R_2} - {R_1})$
  • C$R = {R_2} \times ({R_1} + {R_2})/({R_2} - {R_1})$
  • D$R = {R_2} - {R_1}$
AIEEE 2005,AIIMS 2008, Diffcult
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