The resistance of an ideal \( p \)-\( n \) junction diode in forward bias is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → zero
An ideal diode acts as a perfect switch: it conducts with no voltage drop in forward bias and blocks completely in reverse bias. So its resistance is zero in forward bias and infinite in reverse bias.
Why the other options are incorrect
Option (1) a few ohms — Incorrect. A few ohms (up to some tens of ohms) is the forward resistance of a real diode.
Option (2) a few kilo-ohms — Incorrect. A few kilo-ohms is not the forward resistance of either an ideal or a real diode.
Option (4) infinite — Incorrect. Infinite resistance is the ideal diode in reverse bias.