In the following circuits `PN`-junction diodes `D_(1), D_(2)` and `D_(3)` are ideal for the following potential of `A` and `B`, the correct increasing order to resistance between `A` and `B` will be

`(i) -10V, -5V (ii) -5V,-10V`
`(iii) -4V, -12V`

Options

A. `(i)lt(ii)lt(iii)`
B. `(iii)lt(ii)lt(i)`
C. `(ii)=(iii)lt(i)`
D. `(i)=(iii)lt(ii)`

Answer

C

Explanation

`(i) V_(A)=-10 V` and `V_(B)=-5V`
Diodes `D_(1)` and `D_(2)` are reverse biased and `D_(2)` is forward biased.

`implies R_(AB)=R/4+R/2+R/4=R`
(ii) When `V_(A)=-5V` and `V_(B)=-10 V`
Diodes `D_(1)` is reverse biased `D_(1)` and `D_(3)` are forward biased.

`implies R/4+R/2+R/4=R. =R`
(iii) In this case equivalent resistance between `A` and `B` is also `R`.
Hence `(ii)=(iii)lt(i)`.