Question

Find the currents through the resistance in the circuits shown in figure.

Answer 1

We know that under forward bias, an ideal diode acts as a short circuit; and under reverse bias, an ideal diode acts as an open circuit.

(a) Since both the diodes are forward biassed, they can be replaced by short circuits.
Net resistance = 2 Ω
$i=\frac{2\mathrm{V}}{2\mathrm{\Omega }}=1\mathrm{A}$

(b) One diode is forward biassed and the other is reverse biassed; thus, the resistance of one becomes ∞. The circuit becomes open at the position of the second diode, so no current flows through this arm.
$\therefore i=\frac{2}{2+\infty }=0\mathrm{A}$

(c) Both of them are forward biassed. Thus, the resistance is zero.
We can replace both the resistors by short circuits.
Net resistance = 2 Ω
$\therefore i=\frac{2}{2}=1\mathrm{A}$

(d) One of them is forward biassed and the other is reverse biassed.
Thus, the current passes through the forward-biassed diode and the other acts as open circuit.
$\therefore i=\frac{2}{2}=1\mathrm{A}$