Q. In a combinational circuit, what does the term 'propagation delay' refer to?
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A.
Time taken for the output to stabilize
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B.
Time taken for the input to change
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C.
Time taken for the circuit to power on
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D.
Time taken for the circuit to reset
Solution
Propagation delay is the time taken for the output to stabilize after the input has changed.
Correct Answer:
A
— Time taken for the output to stabilize
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Q. In a combinational circuit, what is the primary function of multiplexers?
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A.
To perform arithmetic operations
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B.
To select one of many inputs
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C.
To store data
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D.
To invert signals
Solution
Multiplexers are used to select one of many input signals and forward the selected input to a single output line.
Correct Answer:
B
— To select one of many inputs
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Q. In a combinational logic circuit, what is the primary function of multiplexers?
-
A.
To perform arithmetic operations
-
B.
To select one of many inputs
-
C.
To store data
-
D.
To invert signals
Solution
Multiplexers are used to select one of many input signals and forward the selected input to a single output line.
Correct Answer:
B
— To select one of many inputs
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Q. In a half adder, what does the sum output represent?
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A.
Carry out
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B.
Logical AND
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C.
Logical OR
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D.
XOR of inputs
Solution
The sum output of a half adder represents the XOR of the two input bits.
Correct Answer:
D
— XOR of inputs
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Q. What is the function of a decoder in combinational logic?
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A.
To encode data
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B.
To convert binary to decimal
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C.
To select a specific output line
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D.
To perform addition
Solution
A decoder converts binary input into a unique output line, effectively selecting one of many outputs based on the input combination.
Correct Answer:
C
— To select a specific output line
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Q. What is the main characteristic of combinational logic circuits?
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A.
Output depends on past inputs
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B.
Output depends only on current inputs
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C.
Output is always constant
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D.
Output is random
Solution
In combinational logic circuits, the output depends only on the current inputs, not on past inputs.
Correct Answer:
B
— Output depends only on current inputs
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Q. What is the output of a 2-input NAND gate when both inputs are low?
-
A.
0
-
B.
1
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C.
Undefined
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D.
Depends on the circuit
Solution
A NAND gate outputs high (1) when at least one input is low (0).
Correct Answer:
B
— 1
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Q. What is the output of a 2-input NOR gate when both inputs are high?
-
A.
0
-
B.
1
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C.
Both 0 and 1
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D.
Undefined
Solution
A 2-input NOR gate outputs 0 when at least one of its inputs is high; it only outputs 1 when both inputs are low.
Correct Answer:
A
— 0
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Q. What is the output of a 2-input NOR gate when both inputs are low?
-
A.
0
-
B.
1
-
C.
Undefined
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D.
Depends on the circuit
Solution
A NOR gate outputs high (1) only when both inputs are low (0).
Correct Answer:
B
— 1
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Q. What is the output of a 2-input XOR gate when both inputs are the same?
-
A.
0
-
B.
1
-
C.
Undefined
-
D.
Depends on the circuit
Solution
An XOR gate outputs low (0) when both inputs are the same (either both 0 or both 1).
Correct Answer:
A
— 0
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Q. What is the purpose of a full adder in digital circuits?
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A.
To add two binary numbers
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B.
To add three binary numbers
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C.
To perform subtraction
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D.
To perform multiplication
Solution
A full adder adds three binary digits, including carry from a previous addition.
Correct Answer:
B
— To add three binary numbers
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Q. What is the truth table output for a 2-input XOR gate when both inputs are the same?
-
A.
0
-
B.
1
-
C.
Both 0 and 1
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D.
Undefined
Solution
A 2-input XOR gate outputs 0 when both inputs are the same (either both 0 or both 1).
Correct Answer:
A
— 0
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Q. Which logic gate outputs true only when at least one input is true?
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A.
AND
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B.
OR
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C.
NOT
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D.
NAND
Solution
An OR gate outputs true (1) when at least one of its inputs is true (1).
Correct Answer:
B
— OR
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Q. Which of the following circuits can be used to implement a full adder?
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A.
AND, OR, NOT gates
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B.
NAND gates only
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C.
XOR gates only
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D.
OR gates only
Solution
A full adder can be implemented using AND, OR, and NOT gates.
Correct Answer:
A
— AND, OR, NOT gates
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