Digital Electronics Logic Gates Questions and Answers
Digital Electronics Logic Gates questions with answers form the base of circuit design and digital systems. Students preparing for GATE, DRDO, and BARC exams must understand AND, OR, NOT, NAND, NOR, XOR, and XNOR gate operations. Practicing these electronics MCQs improves problem-solving accuracy in truth tables, Boolean algebra, and logic circuit simplification. These programming-style questions with explanations are ideal for both technical interviews and competitive electronics exams.
Covers types and functions of logic gates. Complement with digital electronics combinational logic circuits and boolean algebra
Digital Electronics Logic Gates
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78 questions
21. How many inputs of a four-input AND gate must be HIGH in order for the output of the logic gate to go HIGH?
- any one of the inputs
- any two of the inputs
- any three of the inputs
- all four inputs
22. If the output of a three-input AND gate must be a logic LOW, what must the condition of the inputs be?
- All inputs must be LOW.
- All inputs must be HIGH.
- At least one input must be LOW.
- At least one input must be HIGH.
23. Logically, the output of a NOR gate would have the same Boolean expression as a(n):
- NAND gate immediately followed by an inverter
- OR gate immediately followed by an inverter
- AND gate immediately followed by an inverter
- NOR gate immediately followed by an inverter
24. A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?
- The dim indication on the logic probe indicates that the supply voltage is probably low.
- The output of the gate appears to be open.
- The dim indication is the result of a bad ground connection on the logic probe.
- The gate is a tristate device.
25. What is the Boolean expression for a three-input AND gate?
- X = A + B + C
- X = A · B · C
- A – B – C
- A $ B $ C
26. Which of the following gates has the exact inverse output of the OR gate for all possible input combinations?
- NOR
- NOT
- NAND
- AND
27. What is the difference between a 7400 and a 7411 IC?
- 7400 has two four-input NAND gates; 7411 has three three-input AND gates
- 7400 has four two-input NAND gates; 7411 has three three-input AND gates
- 7400 has two four-input AND gates; 7411 has three three-input NAND gates
- 7400 has four two-input AND gates; 7411 has three three-input NAND gates
28. The output of an exclusive-OR gate is HIGH if ________.
- all inputs are LOW
- all inputs are HIGH
- the inputs are unequal
- none of the above
29. A clock signal with a period of 1 s is applied to the input of an enable gate. The output must contain six pulses. How long must the enable pulse be active?
- Enable must be active for 0 s.
- Enable must be active for 3 s.
- Enable must be active for 6 s.
- Enable must be active for 12 s.
30. The AND function can be used to ________ and the OR function can be used to ________ .
- enable, disable
- disable, enable
- enable or disable, enable or disable
- detect, invert