Question

For a two input AND gate, the four entries are shown in the truth table. Identify the correct ones out of these ($A$, $B = $ input, $Y = $ output)

Choose the correct answer from the options given below

• A. 1 and 2 only
• B. 1, 2 and 3 only
• C. 1, 3 and 4 only
• D. 2 and 4 only

Hint:

Think of an AND gate as a multiplication circuit or two electrical switches connected in series. The output circuit can only close and turn on when both switch A AND switch B are completely closed ($1$).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The problem asks us to evaluate four operational entries in a given truth table for a standard two-input AND logic gate and determine which combinations are technically correct.

Step 2: Key Formula or Approach:
The boolean expression representing the operation of a two-input AND gate is:
$$Y = A \cdot B$$ An AND gate output is HIGH ($1$) if and only if all its inputs are simultaneously HIGH ($1$). If any input is LOW ($0$), the output is automatically LOW ($0$).

Step 3: Detailed Explanation:
Let's systematically test each of the four truth table entries against the boolean multiplication rule:
1.

Entry 1: Inputs $A = 0, B = 1$. Output $Y = 0 \cdot 1 = 0$. This entry is

correct.
2.

Entry 2: Inputs $A = 1, B = 0$. Output $Y = 1 \cdot 0 = 0$. This entry is

correct.
3.

Entry 3: Inputs $A = 1, B = 1$. Output $Y = 1 \cdot 1 = 1$. This entry is

correct.
4.

Entry 4: Inputs $A = 0, B = 0$. Output $Y = 0 \cdot 0 = 0$. However, the table entry lists $Y = 1$, which makes this entry

incorrect.
Reviewing our findings, entries 1, 2, and 3 are correct, while entry 4 is false.

Step 4: Final Answer:
The correct entries are 1, 2 and 3 only, which matches option (B).