On connecting a device X in a series circuit with a battery and a resistor, a current passes through the circuit. On reversing the polarity of the battery, the current in the circuit drops to almost zero. The device X may be a
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → p-n junction diode
The device conducts for one polarity of the battery and almost not at all for the other, so it is a one-way device with a rectifying action.
Option (1) p-type semiconductor — Incorrect. A piece of p-type semiconductor is just a resistor, which conducts equally for both polarities.
Option (2) n-type semiconductor — Incorrect. A piece of n-type semiconductor also conducts equally for both polarities.
Option (3) p-n junction diode — Correct. A p-n junction diode conducts in forward bias and gives almost zero current in reverse bias.
Option (4) capacitor — Incorrect. A capacitor blocks a steady dc current for both polarities after charging.
Note: A similar question was also asked in CUET (UG) 2023 on 23-05-2023 (Slot 3).
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. So if an alternating voltage is applied across a diode the current flows only in that part of the cycle when the diode is forward biased.”