Question

Assertion (A) : On forward biasing a p-n junction diode, the height of the barrier potential increases.
Reason (R) : In forward biasing of a p-n junction diode, the direction of the applied voltage is in the same direction as the built-in potential.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false and Reason (R) is also false.

Hint:

Forward bias always means "fighting" the barrier (reducing its height to let current through). Reverse bias means "reinforcing" the barrier (making it taller to block current).

Answer 1

The Correct Option is D

Concept:
• A standard semiconductor p-n junction inherently possesses a narrow depletion region strictly depleted of mobile charge carriers, maintaining a built-in potential barrier that fiercely opposes further natural diffusion.

• The built-in electric field consistently points stubbornly from the n-region (which has exposed positive donor ions) towards the p-region (which has exposed negative acceptor ions).

• Forward biasing is actively achieved by tightly connecting the external battery's positive terminal directly to the p-type region and the negative terminal to the n-type region.

• This specific external battery arrangement forces an external electric field that directly and aggressively opposes the internal built-in field, fundamentally weakening it.

Step 1: Evaluate the Assertion (A)
The assertion firmly claims that applying a forward bias actually increases the overall height of the internal barrier potential.
As detailed in the core concept, applying a forward bias inherently forces the majority carriers from both the p and n sides to aggressively rush towards the central junction.
This aggressive influx effectively shrinks the physical width of the depletion region.
Consequently, the net effective barrier potential is mathematically reduced from $V_0$ down to $(V_0 - V_{applied})$.
Because the barrier height is actually drastically reduced, allowing current to flow easily, the Assertion (A) is entirely physically false.

Step 2: Evaluate the Reason (R)
The reason claims that during forward biasing, the direction of the newly applied external voltage perfectly aligns in the exact same direction as the internal built-in potential.
Let's trace the fields carefully.
The internal built-in potential always directs from the n-side securely to the p-side.
In forward bias, the positive battery terminal connects to the p-side, and the negative to the n-side.
This rigorously creates an applied external electric field directing entirely from the p-side straight to the n-side.
Clearly, the applied field and the built-in field are pointing in perfectly opposite, anti-parallel directions, relentlessly fighting each other.
Therefore, the Reason (R) makes a fundamentally incorrect claim and is completely false.

Step 3: Conclusion
Both the Assertion and the Reason are riddled with fundamental physical errors regarding the basic operation of diodes. Therefore, both are entirely false, pointing strictly to option (D).