## Digital Electronics & Logic Gates Multiple Choice Questions

**Question 1. The most significant digit of the number 6789 is**

- 6
- 7
- 8
- 9

**Answer:** 1. 6

**Question 2. The most significant digit of the number, 0.6789 is**

- 6
- 7
- 8
- 9

**Answer:** 1. 6

**Question 3. The least significant digit of the number, 0.6789 is**

- 6
- 7
- 8
- 9

**Answer: ** 4. 9

**Question 4. In the Binary number system, the number 100 represents **

- One
- Three
- Four
- Hundred

**Answer:** 3. Four

**Question 5. The gate is equivalent to**

- NAND gate
- NOT gate
- AND gate
- NOR gate

**Answer:** 2. NOT gate

**Question 6. In the case of the given circuit, the values of Y _{1}, Y_{2,} and K, are, respectively**

- 1, 1 and 0
- 1,1 and 1
- 1,0 and 0
- 0,1 and 1

**Answer:** 1. 1, 1 and 0

**Question 7. The following truth table is for which gate?**

- AND gate
- NOR gate
- NAND gate
- OR gate

**Answer:** 4. OR gate

**Question 8. The output of an OR gate will be 1, if**

- Both the inputs are 0
- One or both of the inputs be 1
- Both the inputs are 1
- One or both of the input be 0

**Question 9. For which gate is the truth table valid?**

- AND gate
- NOR gate
- NAND gate
- OR gate

**Answer:** 2. NOR gate

**Question 10. According, to the given table, which gate?**

- Gate no. 1
- Gate nos. 1 and 2
- Gate no. 2
- Gate no. 3

**Answer:** 3. Gate no. 2

**Question 11. Digital signals**

- Represent values as discrete steps
- Do not represent values as discrete steps
- Represent vague steps
- represent random steps

**Answer:** 1. Represent values as discrete steps

**Question 12. In Boolean algebra, A + B = Y implies that:**

- The Sum of A and B is Y
- Y exists when A exists or B exists or both A and B exist
- Y exists only when A and B both exist
- Y exists when A or B exists, but not when both A and B exist

**Answer:** 3. Y exists only when A and B both exist

**Question 13. In Boolean algebra, A – B = Y implies that:**

- Product of A and B is Y
- Y exists when A exists or B exists
- Y exists when both A and B exist, but not when only A or B exists
- Y exists when A or B exists, but not both A and B exist

**Answer:** 3. Y exists when both A and B exist but not when only A or B exists

**Question 14. In a three-input logic gate, the first two inputs are in state 1 and the third is 0. For which of the following gates, does the out become 1?**

- OR gate
- And gate
- NOR gate
- NAND gate

**Answer:** 1 And 4

**Question 15. A correct Boolean algebraic equation is**

- A + 0 = 0
- A + 0 = A
- A + 1 = 1
- A + 1 = A

**Answer:** 2 And 3

**Question 16. The product of (110) _{2} and (100)_{2 }is**

- (1100)
_{2} - (11000)
_{2} - (20)
_{210} - (24)
_{10}

**Answer:** 2 And 4

**Question 17. If A and H are the two inputs of a NAND) gate, then the output will be**

- \(\overline{A B}\)
- \(\bar{A} \cdot \bar{B}\)
- \(\overline{A+B}\)
- \(\bar{A}+\bar{B}\)

**Answer:** 1 And 4

**Question 18. The outputs of a three-input OR gate and a three-input NAND gate will be the same if all t**

- Three inputs become 0
- One input becomes 1
- Two inputs become 1
- All three inputs become 1

**Answer:** 2 And 3

**Question 19. If a, b, c, d are input to a gate and r is its output, then, as per the following time graph, the gate is**

- NOT
- AND
- OR
- NAND

**Answer:** 3. OR

**Question 20. Which logic gate is represented by the following combination of logic gates**

- OR
- NAND
- AND
- NOR

**Answer:** 3. OR

Y = \(\overline{Y_1+Y_2}\)

= \(\overline{\bar{A}+\bar{B}}=\overline{\bar{A}} \cdot \overline{\bar{B}}\)

= A.B

The given combination of logic gates represents the AND gate.

**Question 21. To get output 1 for the following circuit, the correct choice for the input is**

- A =1, B = 0, C = 0
- A = 1, B = 1, C = 0
- A = 1, B = 0, C = 1
- A = 0, B = 1, C = 0

**Answer:** 3. A = 1, B = 0, C = 1

The Boolean expression for the given logic circuit is

Y = (A + R). C

If A = 1, B = 0 and C = 1, then the output, Y = 1

**Question 22. From the circuit of the following logic gates, the basic logic gate obtained Is**

- NAND gate
- AND gate
- OR gate
- NOT gate

**Answer:** 1. NAND gate

Y = \(\overline{\bar{A}+\bar{B}}\) = AB

Y = \(\overline{A B \cdot B}=\overline{A B}\) ,NAND gate

**Question 23. In the combination of the following gates, the output Y can be written In terms of inputs A and B as**

- \(\overline{A \cdot B}+A \cdot B\)
- \(A \cdot \bar{B}+\bar{A} \cdot B\)
- \(\overline{A \cdot B}\)
- \(\overline{A+B}\)

**Answer: **2. \(A \cdot \bar{B}+\bar{A} \cdot B\)

Y = \(A \cdot \bar{B}+\bar{A} \cdot B\)

**Question 24. The output Y of the logic circuit Is given below**

- \(\bar{A}+B\)
- \(\bar{A}\)
- \((\overline{\bar{A}+B}) \cdot \bar{A}\)
- \((\overline{\bar{A}+B}) \cdot A\)

**Answer:** 2. \(\bar{A}\)

Y = \(\bar{A}+\bar{A} B=\bar{A}(1+B)=\bar{A}\)

Since 1+ B = 1

**Question 25. The inputs to the digital circuit are shown below the output Y is**

- A+B+\(\bar{C}\)
- (A+B)\(\bar{C}\)
- \(\bar{A}+\bar{B}+\bar{C}\)
- \(\bar{A}+\bar{B}+C\)

**Answer:** 3. \(\bar{A}+\bar{B}+\bar{C}\)

If the Input is the rightmost OR gate is M and N,

Y = M+n = \(\overline{A B}+\bar{C}=\vec{A}+\vec{B}+\vec{C}\)

**Question 26. In the given circuit, the binary Inputs at A and B are both I In one case and both 0 In the next case. The respective outputs at Y In these two cases will be**

- 1,1
- 0,1
- 0,1
- 1,0

**Answer:** 2. 0,0

Y= \(\overline{A \cdot B+\bar{A} \cdot \bar{B}}\)

**Question 27. In the circuit shown, inputs A and B are in states 1 and 0 respectively. What is the only possible stable state of the outputs X and Y?**

- X = 1, Y = 1
- X = 1, Y = 0
- X = 0, Y = 1
- X = 0, Y = 0

**Answer:** 3. X = 0, Y = 0

Given, A = 1 and B = 0,

If X = 1, then Y will be 1. At that instant, the state of X should be 0

But it is given that X = 1.

The option is not correct.

Only they correctly describe the circuit.

Hence, if X = 0, then Y will be 1. At that Instant, X = 0.