Out of the diodes shown in the following diagram which is reverse biased?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2)
A p-n junction diode is forward biased when its p-side (the triangle’s base, the anode) is at a higher potential than its n-side (the bar, the cathode), and reverse biased when it is lower. No current flows through the resistor in the reverse case, so the n-side sits at the potential of the terminal beyond R.
In the diode of Option (2) the anode is connected to the earth (0 V) and the cathode, through R, to \( +5\,\mathrm{V} \). The p-side is at 0 V and the n-side at \( +5\,\mathrm{V} \), so the p-side is at the lower potential and the diode is reverse biased.
Why the other options are incorrect
Option (1) — Incorrect. The p-side (\( -5\,\mathrm{V} \)) is higher than the n-side (\( -16\,\mathrm{V} \)), so the diode is forward biased.
Option (3) — Incorrect. The p-side is at 0 V and the n-side, through R, at \( -10\,\mathrm{V} \). The p-side is higher, so the diode is forward biased.
Option (4) — Incorrect. The p-side is at \( +15\,\mathrm{V} \) and the n-side, through R, at \( +10\,\mathrm{V} \). The p-side is higher, so the diode is forward biased.
NCERT (2026-27):
p-n Junction Diode Under Reverse Bias – “When an external voltage (V ) is applied across the diode such that n-side is positive and p-side is negative, it is said to be reverse biased [Fig.14.15(a)].”