WBCHSE Class 12 Physics Digital Electronics & Logic Gates Multiple Choice Questions

Digital Electronics & Logic Gates Multiple Choice Questions

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

  1. 6
  2. 7
  3. 8
  4. 9

Answer: 1. 6

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

  1. 6
  2. 7
  3. 8
  4. 9

Answer: 1. 6

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

  1. 6
  2. 7
  3. 8
  4. 9

Answer:  4. 9

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

  1. One
  2. Three
  3. Four
  4. Hundred

Answer: 3. Four

Question 5. The gate is equivalent to

Digital Circuit The Gate Equivalent To NOT Gate

  1. NAND gate
  2. NOT gate
  3. AND gate
  4. NOR gate

Answer: 2. NOT gate

Question 6. In the case of the given circuit, the values of Y1, Y2, and K, are, respectively

Digital Circuit The Values Of Y1 And Y2 And Y3

  1. 1, 1 and 0
  2. 1,1 and 1
  3. 1,0 and 0
  4. 0,1 and 1

Answer: 1. 1, 1 and 0

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

Digital Circuit Which Gate Of Truth Table

  1. AND gate
  2. NOR gate
  3. NAND gate
  4. OR gate

Answer: 4. OR gate

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

  1. Both the inputs are 0
  2. One or both of the inputs be 1
  3. Both the inputs are 1
  4. One or both of the input be 0

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

Digital Circuit Which Gate Of Truth Table Valid

  1. AND gate
  2. NOR gate
  3. NAND gate
  4. OR gate

Answer: 2. NOR gate

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

Digital Circuit Acts Gate Number 1 And 2

Digital Circuit Table According To Which Gate

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

Answer: 3. Gate no. 2

Question 11. Digital signals

  1. Represent values as discrete steps
  2. Do not represent values as discrete steps
  3. Represent vague steps
  4. represent random steps

Answer: 1. Represent values as discrete steps

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

  1. The Sum of A and B is Y
  2. Y exists when A exists or B exists or both A and B exist
  3. Y exists only when A and B both exist
  4. 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:

  1. Product of A and B is Y
  2. Y exists when A exists or B exists
  3. Y exists when both A and B exist, but not when only A or B exists
  4. 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?

  1. OR gate
  2. And gate
  3. NOR gate
  4. NAND gate

Answer: 1 And 4

Question 15. A correct Boolean algebraic equation is

  1. A + 0 = 0
  2. A + 0 = A
  3. A + 1 = 1
  4. A + 1 = A

Answer: 2 And 3

Question 16. The product of (110)2 and (100)2 is

  1. (1100)2
  2. (11000)2
  3. (20)210
  4. (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

  1. \(\overline{A B}\)
  2. \(\bar{A} \cdot \bar{B}\)
  3. \(\overline{A+B}\)
  4. \(\bar{A}+\bar{B}\)

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

  1. Three inputs become 0
  2. One input becomes 1
  3. Two inputs become 1
  4. 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

Digital Circuit Following The Graph Of The Gate

  1. NOT
  2. AND
  3. OR
  4. NAND

Answer: 3. OR

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

Digital Circuit Following The Combination Of Logic Gates

  1. OR
  2. NAND
  3. AND
  4. 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

Digital Circuit Output Circuit

  1. A =1, B = 0, C = 0
  2. A = 1, B = 1, C = 0
  3. A = 1, B = 0, C = 1
  4. 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

Digital Circuit Basic Logic Gates

  1. NAND gate
  2. AND gate
  3. OR gate
  4. NOT gate

Answer: 1. NAND gate

Digital Circuit Basic Logic Gates Obtained

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

Digital Circuit Combination Of The Following Gates The Output Y

  1. \(\overline{A \cdot B}+A \cdot B\)
  2. \(A \cdot \bar{B}+\bar{A} \cdot B\)
  3. \(\overline{A \cdot B}\)
  4. \(\overline{A+B}\)

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

Digital Circuit Combination Of The following Gates The Output Y In Terms

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

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

Digital Circuit Y Of The Logic Circuit.

  1. \(\bar{A}+B\)
  2. \(\bar{A}\)
  3. \((\overline{\bar{A}+B}) \cdot \bar{A}\)
  4. \((\overline{\bar{A}+B}) \cdot A\)

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

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

Since 1+ B = 1

Digital Circuit Y Of The Logic Circuit

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

  1. A+B+\(\bar{C}\)
  2. (A+B)\(\bar{C}\)
  3. \(\bar{A}+\bar{B}+\bar{C}\)
  4. \(\bar{A}+\bar{B}+C\)

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

Digital Circuit Binary Inputs

  1. 1,1
  2. 0,1
  3. 0,1
  4. 1,0

Answer: 2. 0,0

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

Digital Circuit Binary Inputs

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?

Digital Circuit Acts A OR And AND Gates Output X And Y

  1. X = 1, Y = 1
  2. X = 1, Y = 0
  3. X = 0, Y = 1
  4. 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.

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