Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Basic Electricity
Curriculum Theme: Basic Electricity
Previous Lesson: Electromagnetism: Lenz’s Law and Motor Applications.
Topic: Transformers
Subject Matter: Definition, Classification, Operational Principles, and Step-up/Step-down Action of Transformers

Specific Objectives

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

Cognitive Domain:

Define a transformer.
Classify transformers based on voltage transformation and core type.
Explain the operational principle of a transformer.
Differentiate between a step-up and a step-down transformer.

Affective Domain:

Appreciate the importance of transformers in power transmission.
Show interest in learning about electrical devices.

Psychomotor Domain:

Draw and label a simple diagram of a transformer.
Identify the main parts of a transformer from a diagram or model.

Participate actively in class discussions about transformers.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum (Senior Secondary School Physics)
State Unified Scheme of Work (Senior Secondary School Physics)
New School Physics by P.N. Okeke and Anyakoha
https://www.electrical4u.com/transformer/
https://byjus.com/physics/transformers/

Instructional Materials

The teacher will teach this lesson with the aid of:

Transformer diagrams
Sample transformers (if available)
Coils and core models
Charts showing transformer types and action

Rationale for the Lesson

This lesson helps pupils understand how transformers work to change voltage levels in electrical circuits. This knowledge is important for understanding how electricity is transmitted from power stations to consumers and how various electrical appliances function in daily life.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of electricity, including concepts such as current, voltage, magnetism, and electromagnetic induction.

Lesson Content/Board Summary

Transformers

Definition of a Transformer

A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It changes alternating current (AC) voltage levels without changing the frequency.

Parts of a Simple Transformer

A simple transformer consists of the following main parts:

Primary Coil/Winding: The input coil connected to the AC power source.
Secondary Coil/Winding: The output coil where induced voltage appears.
Magnetic Core: Usually made of laminated soft iron, it provides a low-reluctance path for the magnetic flux, linking the primary and secondary coils.

Classification of Transformers

Transformers can be classified based on different criteria:

Based on Voltage Transformation:

Step-up Transformer: Increases the voltage from the primary side to the secondary side (Ns > Np).
Step-down Transformer: Decreases the voltage from the primary side to the secondary side (Ns < Np).

Based on Core Material:

Air-core Transformer: Uses air as the magnetic core.
Iron-core Transformer: Uses a laminated soft-iron core to improve magnetic coupling.

Operational Principles of Transformers

The operation of a transformer is based on the principle of mutual electromagnetic induction:

When an alternating current flows through the primary coil, it produces a continuously changing magnetic flux in the core.
This changing magnetic flux links with the secondary coil through the magnetic core.
According to Faraday’s Law of Electromagnetic Induction, this changing flux induces an electromotive force (EMF) or voltage across the secondary coil.
The induced voltage in the secondary coil is proportional to the rate of change of magnetic flux and the number of turns in the secondary coil.

Basic Transformer Action: Step-up and Step-down Concepts

The voltage transformation in a transformer depends on the ratio of the number of turns in the primary and secondary coils.

The relationship between primary voltage (Vp), secondary voltage (Vs), primary turns (Np), and secondary turns (Ns) is given by:

Vs / Vp = Ns / Np

The following are the concepts for step-up and step-down action:

Step-up Transformer: If the number of turns in the secondary coil (Ns) is greater than the number of turns in the primary coil (Np), then the secondary voltage (Vs) will be greater than the primary voltage (Vp). This transformer “steps up” the voltage. In an ideal transformer, the current decreases proportionally (Is < Ip) to maintain constant power.
Step-down Transformer: If the number of turns in the secondary coil (Ns) is less than the number of turns in the primary coil (Np), then the secondary voltage (Vs) will be less than the primary voltage (Vp). This transformer “steps down” the voltage. In an ideal transformer, the current increases proportionally (Is > Ip) to maintain constant power.

Ideally, power input (VpIp) equals power output (VsIs), neglecting losses.

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 greets the pupils and asks them to recall what they know about electricity and magnetism, then introduces the topic “Transformers” by asking if they have seen devices that change voltage (e.g., phone chargers, power supply units).
Pupils’ Activity: Pupils respond to questions about electricity and magnetism and share their experiences with electrical devices.
Learning Point: Pupils are introduced to the lesson topic and connect it to prior knowledge.

Step 2: Definition and Parts of a Transformer

Time: 5 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher defines a transformer and uses a diagram or model to show and explain its main parts (primary coil, secondary coil, magnetic core).
Pupils’ Activity: Pupils listen, observe the diagrams/models, and note down the definition and parts of a transformer.
Learning Point: Pupils learn the definition and identify the basic components of a transformer.

Step 3: Classification of Transformers

Time: 7 minutes
Teaching Skill: Categorisation/Explanation
Teacher’s Activity: The teacher explains the different ways transformers are classified, focusing on voltage transformation (step-up, step-down) and core material (air-core, iron-core), using charts.
Pupils’ Activity: Pupils listen, ask questions for clarity, and take notes on the different types of transformers.
Learning Point: Pupils understand how transformers are categorised.

Step 4: Operational Principles of Transformers

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the operational principle of a transformer, emphasising mutual induction and Faraday’s Law, possibly using a simple coil and magnet demonstration if available.
Pupils’ Activity: Pupils pay attention to the explanation and demonstration, asking questions to grasp the concept of how a transformer works.
Learning Point: Pupils understand the fundamental principle behind transformer operation.

Step 5: Step-up and Step-down Concepts

Time: 7 minutes
Teaching Skill: Elaboration/Comparison
Teacher’s Activity: The teacher elaborates on the concepts of step-up and step-down transformers, explaining the relationship between primary/secondary turns and voltage/current ratios. The teacher uses examples to illustrate.
Pupils’ Activity: Pupils listen to the explanation, participate in discussions, and try to understand the difference between step-up and step-down actions.
Learning Point: Pupils can differentiate between step-up and step-down transformers and understand their basic action.

Step 6: Diagrammatic Representation and Application

Time: 4 minutes
Teaching Skill: Visualisation/Application
Teacher’s Activity: The teacher draws a simple labelled diagram of a transformer on the board, showing primary/secondary coils and core, and briefly mentions common applications (e.g., power transmission, electronics).
Pupils’ Activity: Pupils observe the diagram, copy it into their notebooks, and note down typical applications.
Learning Point: Pupils can visualise a transformer’s structure and its real-world uses.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Define a transformer.
Mention two ways transformers can be classified.
Briefly explain the operational principle of a transformer.
Differentiate between a step-up and a step-down transformer.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 4 minutes
Teaching Skill: Summarisation/Assignment
Teacher’s Activity: The teacher summarises the key points of the lesson and gives pupils an assignment to draw a labelled diagram of a step-up transformer and list three applications of transformers.
Pupils’ Activity: Pupils listen to the summary and copy the assignment.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Transformer – A static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.
Primary Coil – The input coil of a transformer, connected to the AC power source.
Secondary Coil – The output coil of a transformer, where induced voltage appears.
Step-up Transformer – A transformer that increases voltage from primary to secondary.
Step-down Transformer – A transformer that decreases voltage from primary to secondary.
Electromagnetic Induction – The process of producing an electromotive force across an electrical conductor in a changing magnetic field.
Mutual Induction – The production of an electromotive force in one coil due to the change of current in a nearby coil.

Differentiation

The teacher will provide additional support for struggling pupils through one-on-one explanations and simplified diagrams, while advanced pupils will be encouraged to research real-world applications and efficiency of transformers.

Note for teachers using this lesson plan

Teachers should adapt the lesson content and activities to suit the specific needs and context of their pupils and available resources. Practical demonstrations or visual aids are highly recommended to enhance understanding of abstract concepts.