JEE Main · 2023 · 24 Jan 2023 · Shift 2 · Semiconductors

The lamp is held at $+5$ V through the pair of switches and lights whenever its point stays high. The switches are arranged so that the output is pulled low only when $A_1$ and $B_1$ are both operated together; for the input pairs $(0,0)$, $(0,1)$ and $(1,0)$ the lamp glows, while only $(1,1)$ turns it off. An output that is high in every case except when both inputs are high is the defining behaviour of a NAND gate.