Match List-I with List-II.
| List-I | List-II |
| (A) Zener diode | (I) Heavily doped operates in forward bias |
| (B) Photo diode | (II) No external bias required |
| (C) Solar cell | (III) Heavily doped operates in reverse bias as a voltage regulator |
| (D) Light emitting diode | (IV) Fabricated with a transparent window to allow light to fall on it |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) - (III), (B) - (IV), (C) - (II), (D) - (I)
Each special-purpose p-n junction diode is identified by its bias and its construction.
(A) Zener diode — this matches (III) Heavily doped operates in reverse bias as a voltage regulator. Heavy doping gives a thin depletion layer and a sharp breakdown voltage; in reverse breakdown the voltage stays almost constant over a wide range of current.
(B) Photo diode — this matches (IV) Fabricated with a transparent window to allow light to fall on it. It works in reverse bias, and light falling on the junction through the window generates electron-hole pairs that change the reverse current.
(C) Solar cell — this matches (II) No external bias required. The built-in field of the junction separates the light-generated pairs and the cell itself produces an emf.
(D) Light emitting diode — this matches (I) Heavily doped operates in forward bias. In forward bias electrons and holes recombine at the junction and the energy is released as light.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Zener Diode – “… It is designed to operate under reverse bias in the breakdown region and used as a voltage regulator. … Zener diode is fabricated by heavily doping both p-, and n- sides of the junction.”
Photodiode – “A Photodiode is again a special purpose p-n junction diode fabricated with a transparent window to allow light to fall on the diode. It is operated under reverse bias.”
Light Emitting Diode – “It is a heavily doped p-n junction which under forward bias emits spontaneous radiation.”
Solar Cell – “A solar cell is basically a p-n junction which generates emf when solar radiation falls on the p-n junction. It works on the same principle (photovoltaic effect) as the photodiode, except that no external bias is applied and the junction area is kept much larger for solar radiation to be incident because we are interested in more power.”