question_answer

In the following circuits PN-junction diodes D1, D2 and D3 are ideal for the following potential of A and B, the correct increasing order of resistance between A and B will be (i)       ? 10 V, ? 5V                           (ii) ? 5V, ? 10 V (iii)     ? 4V, ? 12V

A)            (i) < (ii) < (iii)                         

B)            (iii) < (ii) < (i)

C)            (ii) = (iii) < (i)                         

D)            (i) = (iii) < (ii)

Correct Answer: C

Solution :

                   (i) VA = ?10V and VB = ?5V Diodes D1 and D3 are reveres biased and D2 is forward biased. \[\Rightarrow {{R}_{AB}}=R+\frac{R}{4}+\frac{R}{4}=\frac{3}{2}R\]. (ii) When VA = ? 5V and VB = ? 10V Diodes D2 is reverse biased D1 and D3 are forward biased \[\Rightarrow {{R}_{AB}}=\frac{R}{4}+\frac{R}{2}+\frac{R}{4}\]=R. (iii) In this case equivalent resistance between A and B is also R. Hence (ii) = (iii) < (i).