Explore topic-wise MCQs in Digital Electronics.

This section includes 289 Mcqs, each offering curated multiple-choice questions to sharpen your Digital Electronics knowledge and support exam preparation. Choose a topic below to get started.

1.

Consider the following statements:
1. A flip-flop is used to store 1-bit of information.
2. Race-around condition occurs in a JK flip-flop when both the inputs are 1.
3. Master-Slave configuration is used in flip-flops to store 2-bits of information.
4. A transparent latch consists of a D-type flip-flop. Which of the above statements is/are correct?

A. 1 only
B. 1, 3 and 4
C. 1, 2 and 4
D. 2 and 3 only
Answer» D. 2 and 3 only
Discussion
2.

For each of the positive edge-triggered JK flip-flop used in the following figure, the propagation delay is T.
Which of the following waveforms correctly represents the output at Q1?

A. 1
B. 2
C. 3
D. 4
Answer» C. 3
Discussion
3.

Consider the following statements: For a Master-Slave JK flip-flop,
1. the toggle frequency is the maximum clock frequency at which the flip-flop will toggle reliably.
2. the data input must preceds the clock triggering edge transition time by some minimum time.
3. the data input must remain fixed for a given time after, the clock triggering edge transition time for reliable operation.
4. propagation delay time is equal to the rise time and fall time of the data. Which of the above statements is/are correct?

A. 1, 2 and 3
B. 1 and 2 only
C. 2 and 3 only
D. 3 and 4 only
Answer» C. 2 and 3 only
Discussion
4.

In a JK flip-flop we have J = Q and K = 1 (shown in figure). Assuming the flip-flop was initially cleaned and then clocked for 6-pulses, the sequence at the Q will be

A. 010000
B. 011001
C. 010010
D. 010101
Answer» E.
Discussion
5.

The architecture of a PLA device differs from that of a PROM device in the following

A. The former has a fixed OR array while the latter has a programmable OR array
B. The former has a programmable AND array while the latter has a hard-wired AND array.
C. The former has larger number of AND gates in the AND array than the latter for a given number of variables.
D. The latter has a fixed OR array while the former has a programmable OR array.
Answer» B. The former has a programmable AND array while the latter has a hard-wired AND array.
Discussion
6.

A Schmitt trigger

A. Is a digital circuit that produces sinusoidal output regardless of the input waveform
B. Is a digital circuit that produces rectangular output regardless of the input waveform
C. Is a digital circuit that produces a trapezoidal output regardless of the input.
D. None of these
Answer» C. Is a digital circuit that produces a trapezoidal output regardless of the input.
Discussion
7.

Simplify (X + Y) (X + Y)

A. X
B. Y
C. X + X
D. X (1 + Y)
Answer» B. Y
Discussion
8.

The Boolean expression A + B + C is

A. Sum term
B. A literal term
C. A product term
D. A complement term
Answer» E.
Discussion
9.

Which one of the following is not a valid rule of Boolean algebra?

A. A + 1 = 1
B. A =
C.
D. AA = A
E. A + 0 = A
Answer» C.
Discussion
10.

The Boolean expression A BC D is

A. Sum term
B. Product term
C. A literal term
D. Always 1
Answer» B. Product term
Discussion
11.

Determine the values of A, B, C that makes the sum term A + B + C equal to 0

A. A = 1, B = 0, C = 0
B. A = 1, B = 1, C = 0
C. A = 0, B = 0, C = 1
D. All of them
Answer» D. All of them
Discussion
12.

The domain of expression ABCD + AB + CD + B is

A. A and D
B. B only
C. A, B, C, D
D. None of these
Answer» C. A, B, C, D
Discussion
13.

The Boolean expression X = AB + CD represents

A. Two ORs ANDed together
B. A 4-input AND gate
C. Two ANDs ORed together
D. An exclusive OR
Answer» D. An exclusive OR
Discussion
14.

Which of the following capabilities are available in a Universal Shift Register?
1. Shift left
2. Shift right
3. Parallel load
4. Serial add
Select the correct answer from the codes given below:

A. 2 and 4 only
B. 1, 2 and 3
C. 1, 2 and 4
D. 1, 3 and 4
Answer» C. 1, 2 and 4
Discussion
15.

Which of the following measurements can be done using a counter?
1. Pulse duration
2. Interval between two pulses
3. Amplitude of the pulse
4. Rise time of a pulse
Select the correct answer from the codes given below:

A. 1 and 2
B. 2 and 3
C. 1 and 4
D. 2 and 4
Answer» B. 2 and 3
Discussion
16.

Consider the following statements regarding registers and latches:
1. Registers are made of edge-triggered FFs, whereas latches are made from level-triggered FFs.
2. Registers are temporary storage devices whereas latches are not.
3. A latch employs cross-coupled feedback connections.
4. A register stores a binary word whereas a latch does not.
Which of the above statements is/are correct?

A. 1 only
B. 1 and 3
C. 2 and 3
D. 3 and 4
Answer» C. 2 and 3
Discussion
17.

Match the following :
Column I Column II )
(GATE) (Boolean Expression)
A.NOR 1.Y = A, B
B.AND2. Y = A + B
C.NAND 3. Y = A B
D. OR 4.Y = A + B

A. (i) (ii) (iii) (iv)
B. (ii) (iii) (iv) (i)
C. (iii) (i) (ii) (iv)
D. (iv) (i) (iii) (ii)
Answer» E.
Discussion
18.

The Boolean expression for Y in the given logic diagram will be

A. Y = RS
B. Y =
C. Y = R + S
D. Y =
E. +
Answer» E. +
Discussion
19.

The Boolean expression
Y = A B + AC + BC
when simplified, becomes
(A) A (B) B (C) B (D) C

A. B
Answer» E.
Discussion
20.

In the above case Y will be

A. 1
B. 0
C. 1 or 0
D. None of these
Answer» C. 1 or 0
Discussion
21.

Match the following:
Column IColumn II
BooleanIdentities
A. A + B 1. 0
B. 1 + A2. A + B
C. A (A + B) 3. 1
D. A . A 4. A

A. (i) (ii) (iii) (iv)
B. (ii) (iii) (iv) (i)
C. (iii) (iv) (i) (ii)
D. (iv) (i) (ii) (iii)
Answer» C. (iii) (iv) (i) (ii)
Discussion
22.

(X+Y) ( X Z + Z). ( Y + X.Z)
when simplified becomes

A. XYX
B. X+Y+Z
C. XY = YZ + ZX
D. 0
Answer» E.
Discussion
23.

In the circuit shown in Fig. the value of input P goes from 0 1 and that of Q goes from 1 0.
Which waveform represent correct output waveform?

A. Output (a)
B. Output (b)
C. Output (c)
D. Output (d)
Answer» E.
Discussion
24.

The Boolean expression
(A + B) ( A + B + C ) ( A + B + C )
When simplified becomes

A. B(A + C) + ABC
B. A (B + C)
C. ABC
Answer» B. A (B + C)
Discussion
25.

A positive going pulse is applied to an inverter. The time interval from the leading edge of the input to the leading edge of the output is 7 ns. This parameter is

A. Speed power product
B. Propagation delay t
C. Propagation delay t
D.
E. Pulse width
Answer» C. Propagation delay t
Discussion
26.

With reference to the exclusive OR gate with many inputs, consider the following statements
1. Even parity input words produce a low output
2. If the inputs are two, the output is high only when the inputs are different.
3. The gate recognised only words of even parity
4. Odd parity input words produce a low output The only true statements are

A. 1, 2
B. 3, 4
C. 1, 3
D. 2, 4
Answer» B. 3, 4
Discussion
27.

Minimum no. of NAND gates require to implement the logic Y = AB + A + B + C

A. 0
B. 2
C. 3
D. 4
Answer» B. 2
Discussion
28.

In the figure, as long as X1 = 1 and X2 = 1, the output Q remains

A. At 1
B. At 0
C. At its initial value
D. Unstable
Answer» E.
Discussion
29.

Simplified form of ZX + Z XY is

A. Z (
B. + Y)
C. Z + Y
D. Z (X + Y)
E. ZY + X
Answer» D. Z (X + Y)
Discussion
30.

Number of NAND gates are required to realize the function
F = ( X + Y). (Z + W)

A. 3
B. 4
C. 5
D. 6
Answer» C. 5
Discussion
31.

Which of the following are universal gates?
1. NAND
2. NOR
3. XOR
Select the correct answer from the codes given below

A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2, and 3
Answer» B. 1 and 3 only
Discussion
32.

The minimized expression for the given K-map (X = don't care) is

A. A +
B. C
C. B + AC
D. C + AB
E. ABC
Answer» B. C
Discussion
33.

Which the Boolean function
F (X1, X2, X3) = (0,1, 2, 3) + d (4, 5, 6, 7) is minimized?

A. 1
B. 0
C. X
D. X
Answer» B. 0
Discussion
34.

A digital circuit which compares two numbers A3 A2A1 A0 and B3 B2 B1 B0 is shown below. To get the output
X = 0, choose one pair of correct input numbers

A. 1010, 1010
B. 0101, 0101
C. 0010, 0010
D. 1010, 1011
Answer» E.
Discussion
35.

What is the minimum number of NAND gates required to implement A + AB + AB C?

A. 0
B. 1
C. 4
D. 7
Answer» B. 1
Discussion
36.

Assume that only the X and Y logic inputs are available and their complements X and Y are not available. What is the minimum number of two input NAND gates required to implement X Y?

A. 2
B. 3
C. 4
D. 5
Answer» D. 5
Discussion
37.

For the circuit shown below the counter state (Q1 Q0) follow the sequence

A. 00, 01, 10, 11, 00 ..........
B. 00, 01, 10, 00, 01 ..........
C. 00, 01, 11, 00, 01 ..........
D. 00, 10, 11, 00, 10 ..........
Answer» C. 00, 01, 11, 00, 01 ..........
Discussion
38.

Consider the following statements in Johnson counter:
1. A MOD-6 Johnson counter requires 3 FFs.
2. Johnson counter requires decoding gates.
3. To decode each count, one logic gate is used.
Which of the statements given above are correct?

A. 1 and 2
B. 2 and 3
C. 1 and 3
D. 1, 2 and 3
Answer» E.
Discussion
39.

Consider the following statements:
A 4: 16 decoder can be constructed (with enable input) by:
1. Using four 2: 4 decoders (each with an enable input) only
2. Using five 2: 4 decoders (each with an enable input) only
3. Using two 3: 8 decoders (each with an enable input) only
4. Using two 3: 8 decoders (each with enable input) and an inverter.
Which of the statements given above is /are correct?

A. 2 and 3
B. 1 only
C. 2 and 4
D. None of these
Answer» D. None of these
Discussion
40.

Consider the following statements:
1. Minimization using Karnaugh map may not provide unique solution.
2. Redundant grouping in Karnaugh map may result in non-minimized solution.
3. Don't care states of used in Karnaugh map for minimization, the minimal solution is not obtained.
Which of the statements given above are correct?

A. 1, 2 and 3
B. 2 and 3 only
C. 1 and 3 only
D. 1 and 2 only
Answer» E.
Discussion
41.

Consider the following statements:
For 3 input variables a, b, c; a Boolean function y = ab + bc + ca represents:
1. a 3-input majority gate
2. a 3-input minority gate
3. Carry output of a full adder
4. Product circuit for a, b and c
Which of the above statements are correct?

A. 1 and 4 only
B. 2 and 3 only
C. 1 and 3 only
D. 3 and 4 only
Answer» D. 3 and 4 only
Discussion
42.

Which of the following circuits come under the class of combinational logic circuits:
1. Full adder
2. Full subtractor
3. Half adder
4. J-K flip-flop
5. Counter
Select the correct answer from the codes given below

A. 1 only
B. 3 and 4
C. 4 and 5
D. 1, 2 and 3
Answer» E.
Discussion
43.

Consider the following statements: A multiplexer
1. Selects one of the several inputs and transmits it to a single output.
2. Routes the data from a single input to one of many outputs
3. Converts parallel data into serial data
4. Is a combinational circuit
Which of these statements are correct?

A. 1, 2 and 4
B. 2, 3 and 4
C. 1, 3 and 4
D. 1, 2 and 3 Answers with Explanatory
Answer» D. 1, 2 and 3 Answers with Explanatory
Discussion
44.

A digital multiplexer can be used for which of the following?
1. Parallel to serial conversion
2. Many to one switch
3. To generate memory chip select
4. For code conversion
Select the correct answer using the code given below

A. 1, 3 and 4
B. 2, 3 and 4
C. 1 and 2 only
D. 2 and 3 only
Answer» D. 2 and 3 only
Discussion
45.

The Boolean functions can be expressed in canonical SOP (sum of products) and POS (product of sums) form. For the functions, Y = A + BC, which are such two forms

A. Y = (1, 2, 6, 7) and Y = (0, 2, 4)
B. Y = (1, 4, 5, 6, 7) and Y = (0, 2, 3)
C. Y = (1, 2, 5, 6, 7) and Y = (0, 1, 3)
D. Y = (1, 2, 4, 5, 6, 7) and Y= (0, 2, 3, 4)
Answer» C. Y = (1, 2, 5, 6, 7) and Y = (0, 1, 3)
Discussion
46.

In addition of two binary variables A and B results into a SUM and a CARRY output. Consider the following expressions for the SUM and CARRY outputs.
(1) SUM = A. B + A B
(2) SUM = A.B + B.A
(3) CARRY = A. B
(4) CARRY = A + B
Which of the following expressions are correct?

A. 1 and 2
B. 2 and 3
C. 2 and 4
D. 1 and 4
Answer» C. 2 and 4
Discussion
47.

One of the following is not a synchronous input with reference to flip-flops

A. J input in a J-K flip-flop
B. S input in an R-S flip-flop
C. PRESET input in a J-K flip-flop
D. D input in a D flip-flop
Answer» D. D input in a D flip-flop
Discussion
48.

Bistable multivibrator is also known as

A. Binary
B. Flip-flop
C. Eceless Jordan circuit
D. All of these
Answer» E.
Discussion
49.

Astable multivibrator is also known as

A. One shot multivibrator
B. Schmidt trigger
C. Free running multivibrator
D. Gating circuit
Answer» D. Gating circuit
Discussion
50.

Following flip-flop is used to eliminate race around problem

A. RS flip-flop
B. Master Slave JK flip-flop
C. JK flip-flop
D. None of these
Answer» C. JK flip-flop
Discussion