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_(1) R_(2) // (R_(1) + R_(2))`
B. `R = R_(1) R_(2) // (R_(1) - R_(2))`
C. `R = R_(2) xx (R_(1) + R_(2)) // (R_(2) - R_(1))`
D. `R = R_(2) - R_(1)`

Answer

D

Explanation

(d) `i= (2E)/(R + R_(1) + R_(2))`
From cell (2) `E = V + iR_(2) = 0 + iR_(2)`
`implies E = (2E)/(R + R_(1) + R_(2)) xx R_(2) implies R = R_(2) - R_(1)`