The logic gate realised using p-n junction diodes in the given figure is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → OR gate
A p-n junction diode conducts only when it is forward biased. In the figure each input, A and B, is joined to the output y through a diode whose arrow points towards y, and y is connected to the ground through the resistance R. A high input (logic 1) is a positive voltage; a low input (logic 0) is zero voltage.
\( A = 0,\ B = 0: \text{ no diode conducts, no current in R} \Rightarrow y = 0 \)
\( A = 1 \text{ or } B = 1: \text{ that diode is forward biased, current flows through R} \Rightarrow y = 1 \)
\( A = 1,\ B = 1: \text{ both diodes conduct} \Rightarrow y = 1 \)
The output is high when at least one input is high, that is \( y = A + B \). This is the OR gate.
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):
Logic Gates – “… An OR gate has two or more inputs with one output. The logic symbol and truth table are shown in Fig. 14.36. The output Y is 1 when either input A or input B or both are 1s, that is, if any of the input is high, the output is high.”