Lesson Note on Logic Gates: Construction of Truth Table (NOR, XOR, XNOR) for SS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Basic Electronics
Curriculum Theme: Digital Electronics
Previous Lesson: Logic Gates: Construction of Truth Tables (OR, NOR, AND).
Topic: LOGIC GATES
Subject Matter: Meaning of LOGIC GATES, construction of truth table (NOR, XOR, XNOR)

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define logic gates.
• Identify the symbols and Boolean expressions for NOR, XOR, and XNOR gates.
• Explain the function of NOR, XOR, and XNOR gates.

Affective Domain:

• Appreciate the importance of logic gates in electronic circuits.
• Show interest in constructing truth tables for different logic gates.

Psychomotor Domain:

• Construct truth tables for NOR, XOR, and XNOR logic gates.
• Draw the standard symbols for NOR, XOR, and XNOR gates.

Social Domain:

• Collaborate effectively when constructing truth tables.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• Basic Electronics for Senior Secondary Schools by A.O. Okoro

Instructional Materials

The teacher will teach this lesson with the aid of:

• Charts showing different logic gate symbols and their truth tables.
• Whiteboard and markers.

Rationale for the Lesson

Understanding logic gates is important for pupils as they form the fundamental building blocks of all digital electronic devices. This lesson helps pupils grasp how digital circuits process information, which is essential for further studies in electronics and computer science.

Prerequisite/Previous Knowledge

Pupils are expected to have a basic understanding of digital electronics, binary numbers, and simple logic gates like AND, OR, and NOT gates.

Lesson Content/Board Summary

LOGIC GATES

Meaning of Logic Gates

Logic gates are electronic circuits that perform logical operations on one or more binary inputs to produce a single binary output. They are the fundamental building blocks of digital electronic systems.

Types of Logic Gates (Recap)

There are seven basic logic gates:

• AND Gate
• OR Gate
• NOT Gate
• NAND Gate
• NOR Gate
• XOR Gate (Exclusive OR)
• XNOR Gate (Exclusive NOR)

Truth Table Construction

A truth table is a mathematical table used in logic to compute the functional values of logical expressions on all combinations of their inputs. For ‘n’ input variables, there will be 2^n rows in the truth table.

NOR Gate

The NOR gate is a digital logic gate that implements logical NOR. A HIGH output (1) results if all the inputs to the gate are LOW (0); otherwise, the output is LOW (0).

• Symbol:

  Draw the standard symbol for a 2-input NOR gate.

• Boolean Expression: A NOR B = (A+B)’ or NOT (A OR B)
• Truth Table:

Input A | Input B | Output (A NOR B)

0 | 0 | 1

0 | 1 | 0

1 | 0 | 0

1 | 1 | 0

XOR Gate (Exclusive OR)

The XOR gate is a digital logic gate that implements an exclusive OR operation. A HIGH output (1) results if the inputs are different; otherwise, the output is LOW (0).

• Symbol:

  Draw the standard symbol for a 2-input XOR gate.

• Boolean Expression: A XOR B = A⊕B = A’B + AB’
• Truth Table:

Input A | Input B | Output (A XOR B)

0 | 0 | 0

0 | 1 | 1

1 | 0 | 1

1 | 1 | 0

XNOR Gate (Exclusive NOR)

The XNOR gate is a digital logic gate that implements an exclusive NOR operation. A HIGH output (1) results if the inputs are the same; otherwise, the output is LOW (0). It is the inverse of the XOR gate.

• Symbol:

  Draw the standard symbol for a 2-input XNOR gate.

• Boolean Expression: A XNOR B = (A⊕B)’ = AB + A’B’
• Truth Table:

Input A | Input B | Output (A XNOR B)

0 | 0 | 1

0 | 1 | 0

1 | 0 | 0

1 | 1 | 1

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher introduces the topic by asking pupils to recall what they know about basic logic gates like AND, OR, and NOT gates.
Pupils’ Activity: Pupils respond by defining basic logic gates and mentioning their functions.
Learning Point: Pupils recall previous knowledge on logic gates.

Step 2: Meaning of Logic Gates

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines logic gates and explains their role as fundamental building blocks in digital electronics, reviewing the basic types.
Pupils’ Activity: Pupils listen attentively, ask questions for clarity, and take notes on the definition.
Learning Point: Pupils understand the meaning and importance of logic gates.

Step 3: Introduction to NOR Gate

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the function of the NOR gate, draws its symbol, states its Boolean expression, and demonstrates how to construct its truth table using the chart.
Pupils’ Activity: Pupils observe the demonstration, copy the symbol and Boolean expression, and begin to understand the truth table construction for the NOR gate.
Learning Point: Pupils learn the characteristics and truth table of the NOR gate.

Step 4: Introduction to XOR Gate

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the function of the XOR gate, draws its symbol, states its Boolean expression, and demonstrates how to construct its truth table.
Pupils’ Activity: Pupils observe, copy the symbol and Boolean expression, and follow along with the truth table construction for the XOR gate.
Learning Point: Pupils learn the characteristics and truth table of the XOR gate.

Step 5: Introduction to XNOR Gate

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the function of the XNOR gate, draws its symbol, states its Boolean expression, and demonstrates how to construct its truth table.
Pupils’ Activity: Pupils observe, copy the symbol and Boolean expression, and follow along with the truth table construction for the XNOR gate.
Learning Point: Pupils learn the characteristics and truth table of the XNOR gate.

Step 6: Practical Construction of Truth Tables

Time: 5 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher guides pupils through constructing the truth tables for NOR, XOR, and XNOR gates on their own, providing assistance where needed.
Pupils’ Activity: Pupils construct the truth tables for the three gates in their notebooks.
Learning Point: Pupils gain practical experience in constructing truth tables.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define a logic gate.
2. Draw the standard symbols for a NOR gate and an XOR gate.
3. State the Boolean expression for an XNOR gate.
4. Construct the truth table for a 2-input NOR gate.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson and assigns homework to draw the symbols and construct truth tables for other basic logic gates.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their understanding and are given further practice.

Lesson Keywords

• Logic gate – An electronic circuit that performs logical operations on binary inputs.
• NOR gate – A gate that outputs 1 only if all inputs are 0.
• XOR gate – A gate that outputs 1 if the inputs are different.
• XNOR gate – A gate that outputs 1 if the inputs are the same.
• Truth table – A table showing all possible input combinations and their corresponding outputs for a logic gate.
• Boolean expression – An algebraic expression representing the logic function of a gate.

Differentiation

For pupils who grasp the concepts quickly, the teacher can challenge them to analyze the behavior of 3-input logic gates or design simple circuits using the learned gates. For those needing more support, the teacher can provide simplified charts and more one-on-one guidance during truth table construction.

Note for teachers using this lesson plan

Ensure that pupils have a solid understanding of binary numbers (0s and 1s) before introducing logic gates. Use clear, large diagrams for symbols and truth tables. Encourage practical drawing and construction of truth tables to reinforce learning. Emphasize the real-world applications of logic gates in computers and other digital devices.