How are switches wired in order to create a NOR logic circuit?

• A. Two normally-open switches in series
• B. Two normally-closed switches in series
• C. One normally closed switch
• D. Two normally-open switches in parallel

Answer: (B)

NOR outputs true only when both inputs are false, so you realize it with two switches that invert each input and must both be closed to complete the path. Using two normally closed switches controlled by the two inputs, wired in series, achieves this: when both inputs are 0, both switches stay closed and the circuit completes, giving a true output. If either input becomes 1, its switch opens and the path is broken, so the output goes false. This setup implements NOT A AND NOT B, which is NOR of A and B. The other configurations don’t match NOR: two normally open switches in series would require both inputs high to turn on (AND of true values), two normally open switches in parallel would turn on if either input is high (OR), and a single normally closed switch acts as a NOT for one input rather than for two.