A semiconducting device is connected as shown in the figure
A current is found to pass through the circuit. On reversing the polarity of the battery. The current in the circuit drops to almost zero. What is this device?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → a p-n junction diode
The device lets current pass for one polarity of the battery and almost none for the other. This one-way conduction is the property of a p-n junction diode: in forward bias the barrier is lowered and a large current flows; in reverse bias only a tiny current of minority carriers flows.
Option (1) a P-type semiconductor — Incorrect. A p-type semiconductor is a doped piece of one kind; it conducts equally well in both directions, like a resistor.
Option (2) an N-type semiconductor — Incorrect. An n-type semiconductor also has no junction, so reversing the battery only reverses the current, without reducing it.
Option (3) an intrinsic semiconductor — Incorrect. A pure (intrinsic) semiconductor conducts weakly but in the same way for both polarities.
Option (4) a p-n junction diode — Correct. Only a junction between p-type and n-type material conducts in forward bias and blocks in reverse bias.
Note: A similar question was also asked in CUET (UG) 2025 on 13-05-2025 (Slot 2).
NCERT (2026-27):
Application of Junction Diode as a Rectifier – “From the V-I characteristic of a junction diode we see that it allows current to pass only when it is forward biased.”