For the circuit shown in the figure, calculate the equivalent resistance for the two cases given as : (1) `V_(A) gt V_(B) and (2) V_(B) gt V_(A)`. Here consider `D_(1) and D_(2)` to be ideal diodes.

Explanation

(1) When `V_(A)gt V_(B)` then `D_(1)` is in forward bias and `D_(2)` is in reverse bias connection. But second diode is iedeal therefore resistance `R_(2)` of `D_(2)` is infinite. Therefore current is flowing throgh only `D_(1)`, so effective resistance is `R_(1)`.
In this situation total resistance of the circuit,
`R_(AB)=50+0`
`therefore R_(AB)=50Omega`
(2) When `V_(B) gt V_(B)` then, `D_(1)` is in reverse bias and `D_(2)` is in forward bias. Therefore resistance `R_(1)` of `D_(1)` is infinite, so current flowing through `D_(1)` is zero. But effective resistance is only `R_(2)`.
`R._(AB)=50+0`
`therefore R._(AB)=50Omega`