# Logic Gates MCQ Questions & Answers

Logic Gates MCQs : This section focuses on the "Logic Gates". These Multiple Choice Questions (MCQs) should be practiced to improve the Logic Gates skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.

Question 1

What is the Boolean expression for a four-input OR gate?

A. Y = A + B + C + D
B. Y = A· B · C · D
C. Y = A – B – C – D
D. Y = A \$ B \$ C \$ D

Question 2

From the truth table for a three-input NOR gate, what is the only condition of inputs A, B, and C that will make the output X high?

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

Question 3

The logic gate that will have a LOW output when any one of its inputs is HIGH is the:

A. NAND gate
B. AND gate
C. NOR gate
D. OR gate

Question 4

The output will be a LOW for any case when one or more inputs are zero in a(n):

A. OR gate
B. NOT gate
C. AND gate
D. NAND gate

Question 5

A device used to display one or more digital signals so that they can be compared to expected timing diagrams for the signals is a:

A. DMM
B. spectrum analyzer
C. logic analyzer
D. frequency counter

Question 6

Which of the following logical operations is represented by the + sign in Boolean algebra?

A. inversion
B. AND
C. OR
D. complementation

Question 7

The AND function can be used to ________ and the OR function can be used to ________ .

A. enable, disable
B. disable, enable
C. enable or disable, enable or disable
D. detect, invert

Question 8

The output of an OR gate with three inputs, A, B, and C, is LOW when ________.

A. A = 0, B = 0, C = 0
B. A = 0, B = 0, C = 1
C. A = 0, B = 1, C = 1
D. all of the above

Question 9

What does the small bubble on the output of the NAND gate logic symbol mean?

A. open collector output
B. tristate
C. The output is inverted.
D. none of the above

Question 10

The output of an AND gate with three inputs, A, B, and C, is HIGH when ________.

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

Question 11

The power dissipation, PD, of a logic gate is the product of the ________.

A. dc supply voltage and the peak current
B. dc supply voltage and the average supply current
C. ac supply voltage and the peak current
D. ac supply voltage and the average supply current

Question 12

The Boolean expression for a 3-input OR gate is ________.

A. X = A + B
B. X = A + B + C
C. X = ABC
D. X = A + BC

Question 13

The logic gate that will have HIGH or "1" at its output when any one (or more) of its inputs is HIGH is a(n):

A. OR gate
B. AND gate
C. NOR gate
D. NOT operation

Question 14

With regard to an AND gate, which statement is true?

A. An AND gate has two inputs and one output.
B. An AND gate has two or more inputs and two outputs.
C. If one input to a 2-input AND gate is HIGH, the output reflects the other input.
D. A 2-input AND gate has eight input possibilities.

Question 15

Which of the following gates has the exact inverse output of the OR gate for all possible input combinations?

A. NOR
B. NOT
C. NAND
D. AND

Question 16

The basic logic gate whose output is the complement of the input is the:

A. OR gate
B. AND gate
C. inverter
D. comparator

Question 17

How many pins does the 4049 IC have?

A. 14
B. 16
C. 18
D. 20

Question 18

How many truth table entries are necessary for a four-input circuit?

A. 4
B. 8
C. 12
D. 16

Question 19

If the output of a three-input AND gate must be a logic LOW, what must the condition of the inputs be?

A. All inputs must be LOW.
B. All inputs must be HIGH.
C. At least one input must be LOW.
D. At least one input must be HIGH.

Question 20

If a 3-input AND gate has eight input possibilities, how many of those possibilities will result in a HIGH output?

A. 1
B. 2
C. 7
D. 8

Question 21

How many inputs are on the logic gates of a 74HC21 IC?

A. 1
B. 2
C. 3
D. 4

Question 22

The format used to present the logic output for the various combinations of logic inputs to a gate is called a(n):

A. Boolean constant
B. Boolean variable
C. truth table
D. input logic function

Question 23

When reading a Boolean expression, what does the word "NOT" indicate?

A. the same as
B. inversion
C. high
D. low

Question 24

The terms "low speed" and "high speed," applied to logic circuits, refer to the ________.

A. rise time
B. fall time
C. propagation delay time
D. clock speed

Question 25

A single transistor can be used to build which of the following digital logic gates?

A. AND gates
B. OR gates
C. NOT gates
D. NAND gates

Question 26

The output of a NOR gate is HIGH if ________.

A. all inputs are HIGH
B. any input is HIGH
C. any input is LOW
D. all inputs are LOW

Question 27

The output of an exclusive-NOR gate is HIGH if ________.

A. the inputs are equal
B. one input is HIGH, and the other input is LOW
C. the inputs are unequal
D. none of the above

Question 28

CMOS IC packages are available in ________.

A. DIP configuration
B. SOIC configuration
C. DIP and SOIC configurations
D. neither DIP nor SOIC configurations

Question 29

Output will be a LOW for any case when one or more inputs are zero for a(n):

A. OR gate
B. NOT gate
C. AND gate
D. NOR gate

Question 30

The term "hex inverter" refers to:

A. an inverter that has six inputs
B. six inverters in a single package
C. a six-input symbolic logic device
D. an inverter that has a history of failure

Question 31

Which of the following equations would accurately describe a four-input OR gate when A = 1, B = 1, C = 0, and D = 0?

A. 1 + 1 + 0 + 0 = 01
B. 1 + 1 + 0 + 0 = 1
C. 1 + 1 + 0 + 0 = 0
D. 1 + 1 + 0 + 0 = 00

Question 32

Fan-out is specified in terms of ________.

A. voltage
B. current
C. wattage

Question 33

The output of an exclusive-OR gate is HIGH if ________.

A. all inputs are LOW
B. all inputs are HIGH
C. the inputs are unequal
D. none of the above

Question 34

The output of a NOT gate is HIGH when ________.

A. the input is LOW
B. the input is HIGH
C. power is applied to the gate's IC
D. power is removed from the gate's IC

Question 35

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?

A. The dim indication on the logic probe indicates that the supply voltage is probably low.
B. The output of the gate appears to be open.
C. The dim indication is the result of a bad ground connection on the logic probe.
D. The gate is a tristate device.

Question 36

TTL operates from a ________.

A. 9-volt supply
B. 3-volt supply
C. 12-volt supply
D. 5-volt supply

Question 37

What input values will cause an AND logic gate to produce a HIGH output?

A. At least one input is HIGH.
B. At least one input is LOW.
C. All inputs are HIGH.
D. All inputs are LOW.

Question 38

What are the pin numbers of the outputs of the gates in a 7432 IC?

A. 3, 6, 10, and 13
B. 1, 4, 10, and 13
C. 3, 6, 8, and 11
D. 1, 4, 8, and 11

Question 39

The Boolean expression for a 3-input AND gate is ________.

A. X = AB
B. X = ABC
C. X = A + B + C
D. X = AB + C

Question 40

What is the circuit number of the IC that contains four two-input AND gates in standard TTL?

A. 7402
B. 7404
C. 7408
D. 7432

Question 41

How many NAND circuits are contained in a 7400 NAND IC?

A. 1
B. 2
C. 4
D. 8

Question 42

A CMOS IC operating from a 3-volt supply will consume ________.

A. less power than a TTL IC
B. more power than a TTL IC
C. the same power as a TTL IC
D. no power at all

Question 43

The switching speed of CMOS is now ________.

A. competitive with TTL
B. three times that of TTL
C. slower than TTL
D. twice that of TTL

Question 44

What is the name of a digital circuit that produces several repetitive digital waveforms?

A. an inverter
B. an OR gate
C. a Johnson shift counter
D. an AND gate

Question 45

The logic gate that will have HIGH or "1" at its output when any one of its inputs is HIGH is a(n):

A. OR gate
B. AND gate
C. NOR gate
D. NOT gate

Question 46

How many inputs of a four-input AND gate must be HIGH in order for the output of the logic gate to go HIGH?

A. any one of the inputs
B. any two of the inputs
C. any three of the inputs
D. all four inputs

Question 47

One advantage TTL has over CMOS is that TTL is ________.

A. less expensive
B. not sensitive to electrostatic discharge
C. faster
D. more widely available

Question 48

Which of the following choices meets the minimum requirement needed to create specialized waveforms that are used in digital control and sequencing circuits?

A. basic gates, a clock oscillator, and a repetitive waveform generator
B. basic gates, a clock oscillator, and a Johnson shift counter
C. basic gates, a clock oscillator, and a DeMorgan pulse generator
D. basic gates, a clock oscillator, a repetitive waveform generator, and a Johnson shift counter

Question 49

What is the Boolean expression for a three-input AND gate?

A. X = A + B + C
B. X = A · B · C
C. A – B – C
D. A \$ B \$ C

Question 50

Which of the following is not a basic Boolean operation?

A. OR
B. NOT
C. AND
D. FOR

Question 51

A NAND gate has:

A. LOW inputs and a LOW output
B. HIGH inputs and a HIGH output
C. LOW inputs and a HIGH output
D. None of the these

Question 52

Exclusive-OR (XOR) logic gates can be constructed from what other logic gates?

A. OR gates only
B. AND gates and NOT gates
C. AND gates, OR gates, and NOT gates
D. OR gates and NOT gates

Question 53

If a 3-input NOR gate has eight input possibilities, how many of those possibilities will result in a HIGH output?

A. 1
B. 2
C. 7
D. 8

Question 54

Write the Boolean expression for an inverter logic gate with input C and output Y.

A. Y = C
B. Y =

Question 55

How many AND gates are found in a 7411 IC?

A. 1
B. 2
C. 3
D. 4

Question 56

The output of a NAND gate is LOW if ________.

A. all inputs are LOW
B. all inputs are HIGH
C. any input is LOW
D. any input is HIGH

Question 57

The basic types of programmable arrays are made up of ________.

A. AND gates
B. OR gates
C. NAND and NOR gates
D. AND gates and OR gates

Question 58

How many entries would a truth table for a four-input NAND gate have?

A. 2
B. 8
C. 16
D. 32

Question 59

The NOR logic gate is the same as the operation of the ________ gate with an inverter connected to the output.

A. OR
B. AND
C. NAND
D. none of the above

Question 60

If a 3-input OR gate has eight input possibilities, how many of those possibilities will result in a HIGH output?

A. 1
B. 2
C. 7
D. 8

Question 61

The basic logic gate whose output is the complement of the input is the:

A. OR gate
B. AND gate
C. INVERTER gate
D. comparator

Question 62

If a signal passing through a gate is inhibited by sending a low into one of the inputs, and the output is HIGH, the gate is a(n):

A. AND
B. NAND
C. NOR
D. OR

Question 63

When used with an IC, what does the term "QUAD" indicate?

A. 2 circuits
B. 4 circuits
C. 6 circuits
D. 8 circuits

Question 64

A 2-input NOR gate is equivalent to a ________.

A. negative-OR gate
B. negative-AND gate
C. negative-NAND gate
D. none of the above