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
How many NAND circuits are contained in a 7400 NAND IC?
A. 1
B. 2
C. 4
D. 8
Question 2
How many truth table entries are necessary for a four-input circuit?
A. 4
B. 8
C. 12
D. 16
Question 3
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 4
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 5
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 6
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 7
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 8
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 9
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 10
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 11
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
Question 12
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 13
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 14
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 15
CMOS IC packages are available in ________.
A. DIP configuration
B. SOIC configuration
C. DIP and SOIC configurations
D. neither DIP nor SOIC configurations
Question 16
Fan-out is specified in terms of ________.
A. voltage
B. current
C. wattage
D. unit loads
Question 17
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 18
How many AND gates are found in a 7411 IC?
A. 1
B. 2
C. 3
D. 4
Question 19
How many entries would a truth table for a four-input NAND gate have?
A. 2
B. 8
C. 16
D. 32
Question 20
How many input combinations would a truth table have for a six-input AND gate?
A. 32
B. 48
C. 64
D. 128
Question 21
How many inputs are on the logic gates of a 74HC21 IC?
A. 1
B. 2
C. 3
D. 4
Question 22
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 23
How many pins does the 4049 IC have?
A. 14
B. 16
C. 18
D. 20
Question 24
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 25
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 26
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 27
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 28
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 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 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 31
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 32
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 33
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 34
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 35
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 36
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 37
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 38
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 39
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 40
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 41
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 42
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 43
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 44
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 45
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 46
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 47
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 48
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 49
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 50
TTL operates from a ________.
A. 9-volt supply
B. 3-volt supply
C. 12-volt supply
D. 5-volt supply
Question 51
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 52
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 53
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 54
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 55
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 56
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 57
When reading a Boolean expression, what does the word "NOT" indicate?
A. the same as
B. inversion
C. high
D. low
Question 58
When used with an IC, what does the term "QUAD" indicate?
A. 2 circuits
B. 4 circuits
C. 6 circuits
D. 8 circuits
Question 59
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 60
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 61
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 62
Which of the following is not a basic Boolean operation?
A. OR
B. NOT
C. AND
D. FOR
Question 63
Which of the following logical operations is represented by the + sign in Boolean algebra?
A. inversion
B. AND
C. OR
D. complementation
Question 64
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 65
Write the Boolean expression for an inverter logic gate with input C and output Y.
A. Y = C
B. Y =