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MCQEasyJEE 2023Logic Gates

JEE Physics 2023 Question with Solution

Identify the logic gate that is equivalent to the given circuit diagram.

Circuit diagram with two switches A and B, a resistor R to ground, +5V supply at top, and an LED output Y showing glow state.
  • A

    NOR

  • B

    OR

  • C

    NAND

  • D

    AND

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: A circuit diagram is provided.

Find: The logic gate equivalent to the circuit.

The solution states that the circuit diagram represents a NAND gate. It explains that when both switches AA and BB are closed, the output is 00, and in all other cases the output is 11.

This matches the truth table:

ABY=A⋅B‾001011101110\begin{array}{|c|c|c|} \hline A & B & Y = \overline{A \cdot B} \\ \hline 0 & 0 & 1 \\ 0 & 1 & 1 \\ 1 & 0 & 1 \\ 1 & 1 & 0 \\ \hline \end{array}

Hence,

Y=A⋅B‾Y = \overline{A \cdot B}

Therefore, the circuit corresponds to a NAND gate.

Common mistakes

  • Confusing the source answer key with the extracted explanation. The correct answer field says (1) NOR, but the solution describes a NAND truth table. Always compare the truth table with the options before final selection.

  • Assuming that output 11 means the current path is blocked in every switching network. Here the solution states the bulb glows for output 11 in all cases except when both switches are closed. The switching behavior must be read from the circuit, not guessed from gate names.

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