Logic Gates MCQ - Physics MCQ

The output of an AND gate with three inputs is high only when all inputs are high.

• Inputs A, B, and C must all be 1 for the output to be high.
• In this scenario: A = 1, B = 1, C = 1.

Therefore, the correct condition is A = 1, B = 1, C = 1.

An OR gate outputs a HIGH value (1) if any of its inputs is HIGH. In the case of a 3-input OR gate, there are 23=823=8 possible input combinations (since each input can be either LOW (0) or HIGH (1)).

These combinations are:

1. 000
2. 001
3. 010
4. 011
5. 100
6. 101
7. 110
8. 111

Out of these, the only combination that will result in a LOW output is the first one (000), where all inputs are LOW. In all other combinations, at least one of the inputs is HIGH, which will result in a HIGH output from the OR gate.

Therefore, out of the 8 input possibilities,7 will result in a HIGH output.

The correct expression for a 4-input OR gate is:

• Y = A + B + C + D

This means that the output Y will be 1 (true) if at least one of the inputs, A, B, C, or D, is 1.

The NAND gate is a type of digital logic gate. When one input is LOW, the output is HIGH. This behaviour is characteristic of the NAND gate. The gate inhibits signals with a LOW input, ensuring the output remains HIGH.

The solution involves changing a logic 1 to logic 0 and vice versa.

The correct logic gate for this operation is an inverter.

The logic gate shown corresponds to the NOR gate. A NOR gate is a combination of an OR gate followed by a NOT gate. It outputs false when at least one of its inputs is true.

When all inputs are false, the output is true.

This logic gate is a combination of AND and NOT gates. It outputs false only when all inputs are true. For any other input combination, the output is true.

The correct answer is: 

The exclusive OR (XOR) gate is a digital logic gate that outputs true or high only when the inputs are unequal.

• If one input is true (1) and the other is false (0), the output is true (1).
• If both inputs are the same (either true or both false), the output is false (0).

This behaviour is captured by the truth table of an XOR gate.

The correct answer is: 

A 3-input NOR gate produces a high output only when all its inputs are low.

• There are 8 possible input combinations for a 3-input gate.
• These combinations include all permutations of high and low inputs.
• For a NOR gate, only the combination where all inputs are 0 results in a high output.

Therefore, there is 1 combination that gives a high output.