A semiconductor device is connected in series circuit with a battery and resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A p-n junction
A device that lets current pass in one direction and almost stops it in the other shows unidirectional conduction. A p-n junction does this: in forward bias the barrier is lowered and a current flows, while in reverse bias the barrier is raised and only a tiny current of minority carriers (of the order of microamperes) flows.
Option (1) A p-type semiconductor — Incorrect. A piece of p-type material behaves like a resistor; it conducts equally well for either polarity.
Option (2) An intrinsic semiconductor — Incorrect. An intrinsic semiconductor also has no junction, so reversing the battery only reverses the current; its size stays the same.
Option (3) An n-type semiconductor — Incorrect. n-type material, like p-type, conducts in both directions.
Option (4) A p-n junction — Correct. The junction conducts in forward bias and blocks in reverse bias, so the current falls almost to zero when the polarity is reversed.
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.”