Choose the correct circuit for the forward bias of p-n junction diode:
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (D) only
A p-n junction is in forward bias when the p-side is connected to the positive terminal of the battery and the n-side to the negative terminal, so that the external voltage opposes the barrier.
Reading the four circuits: the p-side of the diode is on the left in all of them, and it is joined through the key K to the left terminal of the battery E.
The left terminal of E is marked negative in (A), (B) and (C), and positive in (D).
In (A), (B) and (C) the p-side is joined to the negative terminal and the n-side, through R, to the positive terminal, so the diode is in reverse bias. In (D) the p-side is joined to the positive terminal and the n-side, through R, to the negative terminal, so the diode is in forward bias. Only (D) is correct, which is Option (4).
NCERT (2026-27):
p-n Junction Diode Under Forward Bias – “When an external voltage V is applied across a semiconductor diode such that p-side is connected to the positive terminal of the battery and n-side to the negative terminal [Fig. 14.13(a)], it is said to be forward biased.”