Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 2
Age: 15 years
Duration: 45 minutes
Subject: Basic Electricity
Curriculum Theme: Basic Electricity
Previous Lesson: Resistance: Series and Parallel Connections.
Topic: Resistivity and Conductivity
Subject Matter: Definition of resistivity, definition of conductivity, symbols and units of resistivity and conductivity, experimental verification of resistivity, experimental verification of conductivity

Specific Objectives

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

Cognitive Domain:

Define resistivity and conductivity.
State the symbols and units for resistivity and conductivity.
Explain the factors that affect the resistance of a material.
Describe how resistivity and conductivity can be verified experimentally.

Affective Domain:

Show interest in the experimental demonstration of electrical properties.
Appreciate the importance of resistivity and conductivity in electrical applications.

Psychomotor Domain:

Observe and record results from an experiment demonstrating resistivity and conductivity.
Solve simple problems involving resistivity and conductivity.

Collaborate with peers during observation and discussion of experimental results.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Physics (Senior Secondary Education)
State Unified Scheme of Work for Physics SSS 1
Senior Secondary Physics by P.N. Okeke
New School Physics by P.N. Okeke

Instructional Materials

The teacher will teach this lesson with the aid of:

Wires of different materials (e.g., copper, nichrome)
Wires of different lengths and cross-sectional areas
Measuring instruments (ammeter, voltmeter, ohmmeter, meter rule, micrometer screw gauge)
Power supply (battery)
Connecting wires
Charts showing formulas and units

Rationale for the Lesson

This lesson helps pupils understand why different materials behave differently when electricity flows through them. It enables them to know which materials are good for conducting electricity and which are good for resisting it, which is important for designing and using electrical circuits and appliances in daily life.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of electric current, voltage, resistance, and Ohm’s Law from previous lessons.

Lesson Content/Board Summary

Resistivity and Conductivity

Resistivity (Specific Resistance)

Resistivity is a fundamental property of a material that quantifies how strongly it resists the flow of electric current. It is an intrinsic property of the material, meaning it does not depend on the shape or size of the material, but rather on its nature and temperature.

The resistance (R) of a conductor is directly proportional to its length (L) and inversely proportional to its cross-sectional area (A).

R = ρ(L/A)

Where ρ (rho) is the resistivity of the material.

The following are the symbol and unit for resistivity:

Symbol: ρ (rho)
Unit: Ohm-meter (Ωm)

Factors Affecting Resistance (leading to Resistivity)

The resistance of a conductor depends on:

Length (L): Resistance is directly proportional to length. Longer wires have higher resistance.
Cross-sectional Area (A): Resistance is inversely proportional to cross-sectional area. Thicker wires have lower resistance.
Nature of Material: Different materials have different resistivities. For example, copper has low resistivity (good conductor), while nichrome has high resistivity (used in heating elements).
Temperature: For most conductors, resistance increases with temperature.

Experimental Verification of Resistivity

Resistivity can be verified experimentally by measuring the resistance of different wires and observing how it changes with length, cross-sectional area, and material type.

Varying Length: Keep the material and cross-sectional area constant, and measure resistance for different lengths. A graph of R vs. L will be a straight line through the origin, showing R ∝ L.
Varying Cross-sectional Area: Keep the material and length constant, and measure resistance for different cross-sectional areas (or diameters). A graph of R vs. 1/A will be a straight line through the origin, showing R ∝ 1/A.
Varying Material: Keep length and cross-sectional area constant, and measure resistance for different materials. The resistance will vary, demonstrating that resistivity is material-dependent.

Conductivity

Conductivity is a measure of a material’s ability to conduct electric current. It is the reciprocal of resistivity, meaning that materials with high resistivity have low conductivity, and vice versa.

σ = 1/ρ

Where σ (sigma) is the conductivity of the material.

The following are the symbol and unit for conductivity:

Symbol: σ (sigma)
Unit: Siemens per meter (S/m) or Ohm-meter inverse (Ω⁻¹m⁻¹)

Experimental Verification of Conductivity

Since conductivity is the reciprocal of resistivity, its experimental verification is indirectly achieved through the verification of resistivity. Materials that show low resistance for a given length and area (low resistivity) will inherently show high conductivity.

By comparing the resistance of different materials of the same dimensions, one can infer their relative conductivities. For example, copper (low resistance) is a better conductor than nichrome (high resistance).

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 3 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, reviews the previous lesson on resistance, and asks pupils why some wires get hot when current passes through them, while others do not. The teacher then introduces the topic: “Resistivity and Conductivity.”
Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction of the new topic.
Learning Point: Pupils recall previous knowledge on resistance and are introduced to the new topic.

Step 2: Presentation of Resistivity

Time: 10 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines resistivity, explains its formula (R = ρL/A), and states its symbol and unit. The teacher also discusses the factors that affect the resistance of a material (length, area, nature of material, temperature) relating them to resistivity.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition, formula, symbol, unit, and factors influencing resistivity.

Step 3: Experimental Verification of Resistivity

Time: 10 minutes
Teaching Skill: Demonstration/Observation
Teacher’s Activity: The teacher sets up a simple circuit to demonstrate how resistance changes with length and material using different wires and an ohmmeter (or voltmeter and ammeter). The teacher asks pupils to observe and compare the resistance readings.
Pupils’ Activity: Pupils observe the experiment, record observations, and discuss the changes in resistance based on length and material.
Learning Point: Pupils observe the practical factors affecting resistance and understand the concept of experimental verification of resistivity.

Step 4: Presentation of Conductivity

Time: 7 minutes
Teaching Skill: Explanation/Relating Concepts
Teacher’s Activity: The teacher defines conductivity as the reciprocal of resistivity, explains its formula (σ = 1/ρ), and states its symbol and unit. The teacher emphasizes the inverse relationship between resistivity and conductivity and how materials with low resistivity are good conductors.
Pupils’ Activity: Pupils listen, take notes, and understand the relationship between resistivity and conductivity.
Learning Point: Pupils learn the definition, formula, symbol, and unit of conductivity and its relation to resistivity.

Step 5: Class Activity/Practice

Time: 5 minutes
Teaching Skill: Problem Solving
Teacher’s Activity: The teacher writes a simple problem on the board involving the calculation of resistivity or conductivity given relevant parameters. The teacher guides pupils through the solution.
Pupils’ Activity: Pupils attempt to solve the problem individually or in pairs, then discuss the solution as a class.
Learning Point: Pupils apply the formulas for resistivity and conductivity to solve problems.

Step 6: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define resistivity and state its SI unit.
What is conductivity, and how is it related to resistivity?
List two factors that affect the resistance of a wire.
How would you experimentally show that the resistance of a wire depends on its length?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 5 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definitions, symbols, units, and relationship between resistivity and conductivity. The teacher then gives homework, which includes researching practical applications of materials with high and low resistivity.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils reinforce their understanding of the lesson and are encouraged to explore further applications.

Lesson Keywords

Resistivity – A measure of how strongly a material resists the flow of electric current.
Conductivity – A measure of how well a material conducts electric current; the reciprocal of resistivity.
Ohm-meter (Ωm) – The SI unit for resistivity.
Siemens per meter (S/m) – The SI unit for conductivity.
Resistance – Opposition to the flow of electric current.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex problems involving calculations of resistivity and conductivity or ask them to research real-world applications of these properties. For pupils who need more support, the teacher can provide simplified explanations, visual aids, and step-by-step guidance through basic examples, ensuring they understand the core definitions and relationships before moving to calculations.

Note for teachers using this lesson plan

Ensure all instructional materials are prepared and tested before the lesson. Emphasize the practical implications of resistivity and conductivity for everyday devices. Encourage pupils to actively participate in the experimental observation and discussion, making the abstract concepts more concrete.