When a reverse bias is applied to a p-n junction, then

The correct answer is Option (1) → the potential barrier increases

The potential barrier at a p-n junction opposes the diffusion of majority carriers. In reverse bias the p-side is connected to the negative terminal, so the applied voltage V acts in the same direction as the barrier potential \( V_0 \).

    \( V_{\mathrm{barrier}} = V_0 + V \)

The applied field pulls holes and electrons away from the junction, so the depletion layer becomes wider as well.

Why the other options are incorrect

• Option (2) the width of depletion layer decreases — Incorrect. The depletion layer narrows in forward bias; in reverse bias it widens.

• Option (3) the potential barrier decreases — Incorrect. The barrier decreases to \( V_0 - V \) in forward bias, not in reverse bias.

• Option (4) the potential barrier remains unchanged. — Incorrect. The barrier stays at \( V_0 \) only when no bias is applied.

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)]. The applied voltage mostly drops across the depletion region. The direction of applied voltage is same as the direction of barrier potential. As a result, the barrier height increases and the depletion region widens due to the change in the electric field. The effective barrier height under reverse bias is ( \( V_0 + V \) ), [Fig. 14.15(b)].”