Find the correct combination of A, B, C and D inputs which can cause the LED to glow.

Question

G1 Physics · Accepted Answer

The two upper left gates are NOR gates used as NOT gates because each input is effectively applied to both inputs of its gate. Therefore their outputs are Ā and B̄. These feed the next NAND gate. Hence the upper output P is P = overline(ĀB̄) = A + B. The lower gate is a NOR gate with inputs C and D. Therefore, Q = overline(C + D). For the LED to glow in forward bias, the source solution requires P = 1 and Q = 0. Check the options: A B C D = 1 1 0 1 gives P = 1 + 1 = 1, Q = overline(0 + 1) = 0…