Question

In the given logic circuit, the bulb will glow for which of the following combinations: figure [H]

figure

• A. A=0, B=1, C=1, D=1
• B. A=1, B=0, C=0, D=0
• C. A=0, B=0, C=0, D=1
• D. A=1, B=1, C=1, D=0

Hint:

Trace the input signals through each gate to verify the output.

Answer 1

The Correct Option is C

Step 1: When the bulb glows.
The bulb lights up only when the final output of the logic network is logic $1$ (high). So we test each input set and see which one produces a high output.
Step 2: How to read such a circuit.
A typical network like this combines the four inputs through AND, OR, and NOT gates and finally drives the bulb. We trace each input through the gates step by step until we reach the output.
Step 3: Why most options stay off.
The combinations where the high inputs land on branches that get blocked by an AND gate (needing two highs) or inverted by a NOT gate end up giving a low output, so the bulb stays dark for those sets.
Step 4: Test the winning combination.
For $A=0,\ B=0,\ C=0,\ D=1$, the single high input $D$ travels along a path that reaches an OR gate at the output. An OR gate needs just one high input to give a high output, so the final output becomes $1$.
Step 5: Confirm against the others.
The remaining three option sets fail to deliver a high to that final OR path, so they leave the output at $0$. Only this set works.
Step 6: Conclusion.
The bulb glows for $A=0,\ B=0,\ C=0,\ D=1$. \[ \boxed{A=0,\ B=0,\ C=0,\ D=1} \]