Logic Gates AND OR NOT NAND NOR
Chapter: Semiconductor Electronics | Topic: Logic Gates AND OR NOT NAND NOR
LOGIC GATES AND OR NOT NAND NOR
Topic: Logic Gates AND OR NOT NAND NOR
Multiple Choice Questions
Q1. The output of an AND gate is HIGH when:
- Any one input is HIGH
- All inputs are HIGH
- All inputs are LOW
- Only one input is LOW
Q2. The output of an OR gate is LOW when:
- Any one input is HIGH
- All inputs are LOW
- All inputs are HIGH
- Only one input is HIGH
Q3. A NOT gate has:
- One input and one output
- Two inputs and one output
- One input and two outputs
- Two inputs and two outputs
Q4. A NAND gate is equivalent to:
- An AND gate followed by a NOT gate
- An OR gate followed by a NOT gate
- A NOT gate followed by an AND gate
- An AND gate alone
Q5. Which of the following gates is a universal gate?
- AND
- OR
- NAND
- NOT
Q6. The output of a NOR gate is HIGH when:
- Any one input is HIGH
- All inputs are LOW
- All inputs are HIGH
- Only one input is LOW
Short Answer Questions
Q7. Define a logic gate. Name the three basic logic gates and give their symbols.
Q8. Write the truth table for a two-input AND gate.
Q9. Write the truth table for a two-input OR gate.
Q10. What is a universal gate? Name the two universal gates and explain why they are called universal.
Q11. Draw the logic symbol and write the truth table for a NAND gate.
Q12. How can you obtain an AND gate using only NAND gates? Draw the circuit.
Long Answer Questions
Q13. Describe the five basic logic gates (AND, OR, NOT, NAND, NOR) with their symbols, Boolean expressions, and truth tables. Explain how transistor switches can be used to implement these gates.
Q14. Explain why NAND and NOR gates are called universal gates. Show how AND, OR, and NOT gates can be constructed using only NAND gates.
Q15. Discuss the implementation of logic gates using diodes and transistors. Draw the circuit diagram of a diode AND gate and a transistor NOT gate and explain their working.
Numerical & Application-based Problems
Q16. Given the Boolean expression Y = A ยท B + Aฬ ยท Bฬ:
(a) Construct the truth table for this expression.
(b) Draw the logic circuit using AND, OR, and NOT gates.
(c) Simplify the expression if possible.
Q17. Implement the following using only NAND gates:
(a) A NOT gate
(b) An AND gate
(c) An OR gate
(d) Draw the complete circuit for Y = A + B ยท C using only NAND gates.
Q18. In your school computer club, students are learning about digital logic.
(a) A student designs a security system for the school lab using logic gates. The alarm should sound (output = 1) when either the door sensor (A) OR the window sensor (B) is triggered, AND the system is armed (C = 1). Write the Boolean expression and draw the logic circuit.
(b) The student then simplifies the expression Y = A ยท B + A ยท Bฬ + ฤ ยท B. Show the simplification steps and draw the simplified circuit.
(c) She builds a half-adder circuit using logic gates. Draw the circuit using one XOR gate and one AND gate, and verify its truth table for all input combinations.
(d) A classmate claims that any digital circuit can be built using only NAND gates. Verify this by showing how to build an XOR gate using only NAND gates (minimum 4 NAND gates required).
(e) In India, the chip design industry is growing rapidly with companies like Intel, Qualcomm, and indigenous startups. Explain why understanding basic logic gates is essential for VLSI (Very Large Scale Integration) chip design, and how millions of these gates are fabricated on a single silicon chip.