Assuming in forward bias condition there is a voltage drop of 0.7 V across a silicon diode, the current through diode D₁ in the circuit is ____ mA .
(Assume all diodes in the given circuit are identical)

Solution

Physics sir · 4 steps

First check which way each diode points: D2 is reversed, so the current splits between D1 and D3 only.

1. Check each diode. The top rail connects to the positive terminal through R₁, and the bottom rail is at ground. D₁ and D₃ point downward, from the high rail to the low rail, so they are forward biased. D₂ points upward, so it is reverse biased and carries no current.
2. Voltage across R1. The conducting diodes are in parallel, so the voltage between the two rails is fixed at 0.7 V. The resistor takes the rest: 12 - 0.7 = 11.3 V.

   I = (12 - 0.7)/(0.3 kΩ) = (11.3 V)/(300 Ω) ≈ 37.67 mA

3. Split the current. D₁ and D₃ are identical and have the same voltage across them, so they share the current equally. I_(D₁) = 37.67/2 ≈ 18.8 mA.
4. So. The current through D₁ is about 18.8 mA, option (b).

The idea to keep. With parallel diodes, check the arrow of each one before you split the current. A reverse-biased diode drops out, and the resistor takes the supply voltage minus one 0.7 V drop.

Answer from the NTA final answer key. Solution by PrepWiser.