Goa Board Class 12 Question Paper 2025 Digital Electronics & Computers

2025 II 21 0930 Seat No.

Time : 2 Hours DIGITAL ELECTRONICS AND
COMPUTERS

Subject Code

V 4 3 3 1

Total No. of Questions : 23 (Printed Pages : 4) Maximum Marks : 50

INSTRUCTIONS : (i) There are four sections in the question paper (A, B, C & D)
consisting of 23 questions

(ii) In Section A there are eight questions of which question
Nos. 1 to 4 are Multiple Choice Questions, question Nos. 5
& 6 are to be answered in one word, phrase or figure and
question Nos. 7 & 8 are to be answered in one sentence each.

(iii) Attempt all the questions, however internal choice is given
for question numbers 20 and 23.

(iv) Figures to the right indicate marks allotted to each question.

(v) Write the number of each question clearly on the answer
book.

Section A

1. The radix of Octal number system is ...................... . 1

• 2

• 4

• 8

• 16

V-4331 1 P.T.O.

2. The Boolean equation of a 2 input X-OR gate is ...................... . 1

• Y A .B

• Y A B

• Y A.B

• Y A B

3. The IC number of quad two input NAND gate is ...................... . 1

• IC 7402

• IC 7404

• IC 7400

• IC 7408

4. Data of EPROM can be erased by using ...................... . 1

• X-rays

• Alpha rays

• Ultraviolet rays

• Gamma rays

5. Name the circuit used for regenerating distorted pulses. 1

6. What is the 2’s complement of binary number (1000)2 ? 1

7. Define Demultiplexer. 1

8. What is the full form of ALU and CPU ? 1

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Section B

9. What is binary ladder ? Draw a neat logic diagram of 4 bit binary

ladder. 2

10. Define modulus of a Counter. What is the modulus of a 3 bit synchronous

counter ? 2

11. Draw the block diagram of computer system. 2

12. What is a ripple counter ? State any two advantages of it. 2

13. Draw a neat logic diagram of Half Adder and write its truth table. 2

14. What is ‘Accuracy’ and ‘Resolution’ in D to A Converter ? 2

Section C

15. Draw the internal pin configuration diagram of IC 7402. Show how

NOR gate can be converted to OR gate with the help of a neat logic

diagram. 3

16. Distinguish between Astable Multivibrator and Bistable Multivibrator. State

any three points. 3

17. Do as directed : 3

(i) Convert (349)10 to its binary equivalent.

(ii) Convert (7E)16 to its decimal equivalent.

(iii) Subtract (1010)2 from (1101)2.

18. Explain the working of a 4-bit shift left register with the help of a neat logic

diagram. 3

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19. Give three points of difference between impact printers and non-impact

printers. 3

20. State and verify De Morgan’s second theorem with the help of logic diagram

and truth table. 3

Or

With the help of a neat circuit diagram and truth table, explain the working

of 2 input TRL AND gate.

Section D

21. Explain the following devices in brief : 4

(i) Keyboard

(ii) Optical Scanner.

22. State any four points of comparison between 8080A and 8085 micro-

processor. 4

23. Explain the working of positive edge triggered J-K flip-flop with a neat

circuit diagram. 4

Or

Explain the working of Schmitt Trigger with the help of a neat circuit

diagram.

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