Two sources of equal emf are connected to an external resistance R. The internal resistance of the two sources are `R_1 and R_2(R_1gtR_1).` if the potential difference across the source having internal resistance `R_2` is zero, then

Options

A. `R = R_2 - R_1`
B. `R= R_2 xx (R_1 + R_2) // (R_2 - R_1)`
C. `R = R_1 R_2 // (R_2 - R_1)`
D. `R = R_1 R_2 // (R_1 - R_2)`

Answer

A

Explanation

`I= ( 2 epsilon)/( R + R_(1) + R_(2))`
Potential difference across second cell
`= V = epsilon - I R_(2) =0`
`epsilon- (2 epsilon)/( R + R_1 + R_2) R_2 =0`
`R+ R_(1) + R_(2) - 2 R_(2) =0`
`R+ R_(1) - R_(2) = 0`
`therefore R= R_(2) - R_(1)`