JEE Main · 2023 · 06 Apr 2023 · Shift 1 · Semiconductors

The output $Y$ is read through the LED, which glows ($Y=1$) only when current is driven through it. Each switch, when closed (input $=1$), provides a low-resistance path that pulls the output node down through $R$, so the LED cannot glow; closing $A$ or $B$ or both therefore forces $Y=0$. The LED glows only when both switches are open, i.e. $A=0$ and $B=0$. An output that equals $1$ for the single input combination $(0,0)$ and $0$ for every other combination is the truth table of a NOR gate.