Computer Science Test | Chapter 3: Digital Systems and Logic Designs
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Logic Design Test

Class 9th – Computer Science & Entrepreneurship (SNC) – Chapter 3
2025@everexams.com
Paper Date:
Time: 60 minutes
Total Marks: 30
Paper Type: Objective + Subjective
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Multiple Choice Questions 10×1=10

1 Which logic gate outputs true only if both inputs are true?
AND
A OR gate
B AND gate
C XOR gate
D NOT gate
2 What is the output of a NOT gate if the input is 1?
A 0
B 1
C 2
D None of these
3 What is the purpose of a Digital to Analog Converter (DAC)?
A To convert digital signals to analog signals
B To convert analog signals to digital signals
C To amplify digital signals
D To store digital signals
4 Which of the following is NOT a characteristic of digital signals?
A Binary representation
B Continuous waveform
C Both A and B
D None of these
5 What is the main reason for using digital signals in communication systems?
Digital vs Analog: Digital signals are less prone to noise and distortion
A They are easier to generate
B They are less affected by noise
C They require less bandwidth
D They are continuous
6 Which of the following is a disadvantage of digital systems compared to analog systems?
A They are more complex to design
B They are less accurate
C They are slower
D None of these
7 What is the binary representation of the decimal number 10?
A 1010
B 1001
C 1100
D 1111
8 Which of the following is true about analog signals?

Hint: Analog signals are continuous while digital signals are discrete

A They are discrete
B They can have infinite values within a range
C They are used in digital computers
D They are less affected by noise
9 Which of the following is a step in simplifying Boolean expressions using Karnaugh maps?
A Grouping 1s in powers of two
B Grouping 0s in powers of two
C Both A and B
D None of these
10 Which of the following is used to represent a NAND gate in a logic diagram?
AND
NOT
A A triangle with a line
B A rectangle with a straight line
C A circle with a plus sign
D None of these

Short Answer Questions 10×2=20

I Describe the function of a NOT gate with its truth table.
Input Output
0 1
1 0
II What characteristic distinguishes analog signals from digital signals in terms of continuity?
III Convert the binary number 1101 to its decimal equivalent.

Method: Multiply each bit by 2position and sum

IV Draw the symbol for a NAND gate.
V Which law states A+(B·C)=(A+B)·(A+C)?
Distributive Law: A + (B·C) = (A+B)·(A+C)
VI What is the purpose of the Consensus Theorem?
VII Simplify \( \overline{\overline{A}} \) using the Double Negation Law.
VIII How many AND gates are needed to implement (A·B)+(C·D)?
IX What components are required to build a full-adder?
X Sketch the logic diagram for F=A+B·C.

Detailed Answer Questions (Answer any 2) 2×5=10

1 Explain the usage of Boolean functions in computers.

Key Points:
1. Digital circuit design
2. Logic operations
3. Decision making in processors
4. Memory addressing

2 Explain the difference between analog and digital signals with examples.
Analog: Sound waves, temperature readings
Digital: Computer data, digital clocks
3 What is the significance of De Morgan’s theorems in simplifying Boolean expressions?
De Morgan’s Theorems:
\( \overline{A·B} = \overline{A} + \overline{B} \)
\( \overline{A+B} = \overline{A} · \overline{B} \)