Question

In the following circuits P N - junction diodes $D_1$, $D_2$ and $D_3$ are ideal for the following potential of A and B, the correct increasing order of resistance between A and B will be -
i) $-10V,-5V$, II) $-5V,-10V$, III) $-4V,-12V$

• A. $\left(I\right)<\left(II\right)<\left(III\right)$
• B. $\left(III\right)<\left(II\right)<\left(I\right)$
• C. $\left(II\right)=\left(III\right)<\left(I\right)$
• D. $\left(I\right)=\left(III\right)<\left(II\right)$

Answer 1

The correct option is C $\left(II\right)=\left(III\right)<\left(I\right)$

$\left(i\right)V_A=-10V$ and $V_B=-5V$

Diodes $D_1$ and $D_3$ are reverse biased and $D_2$ is forward biased.

$\Rightarrow =R_{AB}=R+\frac{R}{4}+\frac{R}{4}=\frac{3}{2}R$

(ii) When $V_A=-5V$ and $V_B=-10V$

Diodes $D_2$ is reversed biased $D_1$ and $D_3$ are forwards biased.

$\Rightarrow R_{AB}=\frac{AR}{4}+\frac{-RV}{2}+\frac{R}{4}=R$

(iii) In this case equivalent resistance between $A$ and $B$ is also $R$.