In a NOR SR flip-flop, when S = 1 and R = 0, what happens to Q'?

• A. It becomes 1
• B. It becomes 0
• C. Remains unchanged
• D. Oscillates

Answer: (B)

This asks how a NOR SR latch behaves when the set input is activated. A NOR latch is two cross‑coupled NOR gates. When S is high, the NOR gate that includes S as an input cannot output 1 (a NOR gate outputs 1 only if both inputs are 0); with S = 1, its output goes to 0. That 0 is fed back into the other NOR gate, and with R = 0 the second gate sees 0 on both inputs, so it outputs 1. Therefore the output tied to the first gate becomes 0 (the Q' side), and the other output becomes 1 (Q). So Q' goes to 0 while Q goes to 1, matching the set condition.