Question

For the output of the following logic circuit to be '1', the values of inputs A and B should be respectively

• A. 0 and 1
• B. 0 and 0
• C. 1 and 1
• D. 1 and 0

Hint:

A NOR gate outputs a 1 if and only if all of its inputs are completely clear (0). If even a single input is flipped to 1, the internal OR stage triggers, which turns the final inverted output into 0. Thus, 0 and 0 is the unique solution.

Answer 1

The Correct Option is B

Step 1: Identify the combined gate.
An OR gate feeding a NOT gate acts as a single NOR gate, whose output is $Y = \overline{A + B}$. We work backward from the required output.
Step 2: Set the target output.
We need $Y = 1$, so $\overline{A + B} = 1$.
Step 3: Remove the inversion.
Taking the complement of both sides gives $A + B = 0$.
Step 4: Interpret the OR being zero.
An OR result of $0$ is only possible when every input is $0$, since even one $1$ would make the OR equal $1$.
Step 5: Fix the inputs.
Therefore $A = 0$ and $B = 0$.
Step 6: Verify.
With $A = B = 0$: $A + B = 0$, and inverting gives $Y = 1$, matching the requirement. \[ \boxed{A = 0,\ B = 0} \]