Question

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
A. `R = R_2-R_1`
B. `R = R_2 xx (R_1+R_2)//(R_2-R_1)`
C. `R= R_1R_2//(R_2-R_1)`
D. `R = R_1R_2//(R_1-R_2)`

Answer 1

Correct Answer - A
(a)
`I = (2epsilon)/(R+R_1+R_2)`
Potential difference across second cell = V = epsilon - IR_2 = 0 `
`epsilon - (2epsilon)/(R+R_1+R_2) * R_2 = 0`
`R + R_1 + R_2 - 2R_2 = 0`
`R + R_1 -R_2 =0` `:. R = R_2-R_1`.