In the following circuits PN - junction diodes `D_1,D_2 and D_3` are ideal for the following potentials of A and B. The correct increasing order of resistance between A and B will be

(i) `-10V, -5V`
(ii) `-5 V,-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

`V_A=-10V and V_B =-5V`
Diodes `D_1 and D_3` are reverse biased and `D_2 ` is forward biased.

`implies R_(AB)=R+R/4+R/4=3/2R`
(ii) When `V_A = - 5V and V_B = -10 V`
Didoes `D_2` is reverse biased `D_1 and D_3` are forward biased

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