Refer to the logic circuit shown in the figure. Which input combination makes both LED-1 and LED-2 glow simultaneously?

Question

G1 Physics · Accepted Answer

The first gate is an OR gate, so the node driving LED-1 has output Y₁ = A+B. The same OR output and input C enter an AND gate. Its output then enters a final AND gate together with a direct input from A. Therefore LED-2 is driven by Y₂ = A(A+B)C. For both LEDs to glow, we need Y₁ = 1 and Y₂ = 1. The condition Y₂ = 1 requires A = 1, C = 1, and then A+B is automatically 1. Among the given options, only A = 1, B = 0, C = 1 satisfies these conditions. Correct option: C.