# MCQs on Digital Electronics

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01․ What logic function is produced by adding an inverter to each input and output of an OR gate?
NAND
NOR
AND
X-OR

The NOT gates are to be added to the inputs of OR gate, it will give the NAND gate output. Because, bubbled OR gate will acts as a NAND gate. If we add another inverter at output side, it will give the AND gate output.

02․ Which of the following gates is known as a coincidence detector?
AND gate
NAND gate
X-OR gate
X-NOR gate

In X-NOR gate output is ‘1’ when number of 1’s at the input is even number. Therefore X-NOR gate is a even number of 1’s detector. X-NOR gate is also known as coincidence detector or equivalence detector.

03․ Which of the following gates is known as anticoincidence detector?
OR gate
X-OR gate
AND gate
X-NOR gate

In X-OR gate output is ‘1’ when number of 1’s at the input is odd number. Therefore X-OR gate is a odd number of 1’s detector. X-OR gate is also known as anticoincidence detector.

04․ The output of a NOR gate is high
only when all the inputs are low
only when all the inputs are high
only when at least one input is high
only when at least one input is low

NOR gate can be obtained by adding inverter to the OR gate output. The output of OR gate is high when any one of the inputs is high and output of OR gate is low only when all inputs are low. Therefore, the output of NOR gate is high only when all inputs are low.

05․ The output of a NAND gate is low
only when all the inputs are low
only when all the inputs are high
only when at least one input is high
only when at least one input is low

NAND gate can be obtained by adding inverter to the AND gate output. The output of AND gate is high when all the inputs is high and output of AND gate is low only when any one of the inputs is low. Therefore, the output of NAND gate is high only when at least one input is low.

06․ How many NOR gates are required to obtain AND operation?
2
3
4
1

NAND and NOR gates are universal gates. We can realize any gate by using of NAND or NOR gate. The number of NOR gates required for obtain AND gate operation is 3.

07․ What is the minimum number of NAND gates required to realize an X-OR gate?
3
4
5
6

NAND and NOR gates are universal gates. We can realize any gate by using of NAND or NOR gate. The number of NAND gates required to realize X-OR operation is 4. As well as number NOR of gates required to realize X-OR operation is 5.

08․ What is the minimum number of NOR gates required realizing an X-OR gating?
3
4
5
6

NAND and NOR gates are universal gates. We can realize any gate by using of NAND or NOR gate. The number of NAND gates required to realize X-OR operation is 4. As well as number NOR of gates required to realize X-OR operation is 5.

09․ An AND gate can be imagined as
switches connected in series
switches connected in parallel
transistors connected in series
transistors connected in paralle

The output of AND gate is high only when all the inputs are high. Therefore, AND gate can be imagined as switches connected in series. In this case output is high only when all switches are ON.

10․ An OR gate can be imagined as
switches connected in series
switches connected in parallel
transistors connected in series
transistors connected in parallel

The output of OR gate is high only when at least any one of the inputs is high. Therefore, OR gate can be imagined as switches connected in paralell. In this case output is high only at least any one of the swithes is ON.

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