Question

For the circuit shown in the figure, calculate the equivalent resistance for the two cases given as : (1) VA > VB and (2) VB > VA. Here consider D1 and D2 to be ideal diodes.[Ans:For both the cases RAB = 50 Ω]

Answer 1

concept :- The ideal diode has infinite current in forward bias condition. It implies the device acts as pure conductor when forward voltage is applied across it.
The ideal diode has zero current in reverse bias condition. It implies the device has infinite resistance when reverse voltage is applied across it.


solution :- (1) VA > VB
so, we can assume A is postive terminal and B is negative terminal . basically current flows from positive terminal to negative terminal.
now current , i flows from A and divides two part i1 goes from forward bais diodes and reaches at B. but due to reverse baise i2 doesn't reach at B.
hence, in this case current is passing only one wire of resistance 50 ohm.
hence, equivalent resistance in this case is 50ohm.

similarly , we can do in (2) VA < VB
in this case i2 reaches at B , while i1 doesn't .
so, equivalent resistance is also 50ohm in this case .