Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Basic Electricity
Curriculum Theme: Basic Electricity
Previous Lesson: Trans.
Topic: TRANSFORMERS
Subject Matter: transformer efficiency, transformer losses, applications of transformers, calculation of turns ratio, stepping down and stepping up transformer operations

Specific Objectives

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

Cognitive Domain:

Define a transformer and explain its working principle.
State the different types of transformer losses.
List at least three applications of transformers.
Calculate the turns ratio of a transformer given relevant parameters.
Differentiate between step-up and step-down transformer operations.

Affective Domain:

Appreciate the importance of transformers in power transmission and electronic devices.
Show interest in understanding the concepts of transformer efficiency and losses.

Psychomotor Domain:

Demonstrate the calculation of transformer turns ratio.
Observe and describe step-up and step-down transformer actions using a transformer kit.

Participate actively in group discussions and practical demonstrations.
Collaborate with peers to solve problems related to transformer calculations.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary School Physics.
State Unified Scheme of Work for Basic Electricity SSS 1.
Nelkon and Parker, Advanced Level Physics.
https://www.physicsclassroom.com/class/circuits/Lesson-4/Transformers
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/transformer-losses/

Instructional Materials

The teacher will teach this lesson with the aid of:

Transformer kits (primary and secondary coils).
Multimeter.
Power supply (AC source).
Charts illustrating transformer efficiency and types of losses.

Rationale for the Lesson

This lesson helps pupils understand how transformers work, which is important for appreciating how electricity is transmitted and used in various electronic devices. Understanding transformers helps pupils grasp fundamental principles of electrical engineering that are applied in daily life.

Prerequisite/Previous Knowledge

Pupils are expected to have prior knowledge of basic electricity, magnetism, alternating current (AC), and direct current (DC).

Lesson Content/Board Summary

TRANSFORMERS

Definition of a Transformer

A transformer is an electrical device that transfers electrical energy from one circuit to another through electromagnetic induction, usually with a change in voltage and current.

Transformer Efficiency

Transformer efficiency is the ratio of output power to input power, usually expressed as a percentage. It indicates how effectively the transformer converts electrical energy.

Efficiency (η) = (Output Power / Input Power) × 100%

Transformer Losses

Transformer losses are energy dissipations that occur during the operation of a transformer, reducing its efficiency. The following are types of transformer losses:

Copper Loss (I²R Loss): Occurs in the windings due to the resistance of the copper wires.
Eddy Current Loss: Induced currents in the transformer core, causing heating.
Hysteresis Loss: Energy loss due to the repeated magnetization and demagnetization of the transformer core material.
Flux Leakage Loss: Occurs when not all the magnetic flux produced by the primary winding links with the secondary winding.

Applications of Transformers

The following are common applications of transformers:

Stepping up voltage for long-distance power transmission.
Stepping down voltage for domestic and industrial use.
In electronic devices such as chargers, radios, and televisions.
For impedance matching in audio circuits.

Turns Ratio Calculation

The turns ratio of a transformer is the ratio of the number of turns in the secondary coil (N_s) to the number of turns in the primary coil (N_p). It also relates to the ratio of voltages.

Turns Ratio = N_s / N_p = V_s / V_p

Where: V_s = Secondary Voltage, V_p = Primary Voltage.

Step-Up and Step-Down Transformer Operations

Step-Up Transformer: A transformer that increases the output voltage (V_s > V_p) and decreases the current. This happens when the number of turns in the secondary coil is greater than the primary coil (N_s > N_p).
Step-Down Transformer: A transformer that decreases the output voltage (V_s < V_p) and increases the current. This happens when the number of turns in the secondary coil is less than the primary coil (N_s < N_p).

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 if they know how electricity gets from power stations to their homes. The teacher then introduces the topic “Transformers” as a key device in this process and writes it on the board.
Pupils’ Activity: Pupils respond to the questions and pay attention to the introduction of the new topic.
Learning Point: Pupils are prepared for the lesson and understand the relevance of transformers.

Step 2: Definition and Principle of Transformer

Time: 7 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher defines a transformer, explains its basic principle of operation (mutual induction), and sketches a simple diagram of a transformer on the board, pointing out the primary and secondary coils and the core.
Pupils’ Activity: Pupils listen, take notes, and observe the diagram drawn by the teacher.
Learning Point: Pupils understand the definition and basic working principle of a transformer.

Step 3: Transformer Efficiency and Losses

Time: 8 minutes
Teaching Skill: Explanation/Categorization
Teacher’s Activity: The teacher explains transformer efficiency and its formula. The teacher then discusses various types of transformer losses (copper loss, eddy current loss, hysteresis loss, flux leakage loss) using the charts as visual aids.
Pupils’ Activity: Pupils listen, ask questions for clarification, and take notes on the types of losses.
Learning Point: Pupils identify and understand the factors affecting transformer efficiency.

Step 4: Applications of Transformers

Time: 5 minutes
Teaching Skill: Listing/Real-world Connection
Teacher’s Activity: The teacher engages pupils in a discussion about where they might have seen transformers or how they are used, then lists and explains key applications of transformers in power systems and electronic devices.
Pupils’ Activity: Pupils contribute ideas and note down the applications discussed.
Learning Point: Pupils identify practical uses of transformers in everyday life.

Step 5: Turns Ratio Calculation

Time: 8 minutes
Teaching Skill: Calculation/Problem Solving
Teacher’s Activity: The teacher introduces the formula for turns ratio (N_s/N_p = V_s/V_p) and guides pupils through an example calculation. For instance: “A transformer has 200 turns in its primary coil and 1000 turns in its secondary coil. If the primary voltage is 20V, what is the secondary voltage?”
Pupils’ Activity: Pupils copy the formula, follow the example, and attempt to solve similar problems given by the teacher.
Learning Point: Pupils can calculate the turns ratio and related voltages of a transformer.

Step 6: Step-Up and Step-Down Operations Demonstration

Time: 7 minutes
Teaching Skill: Demonstration/Observation
Teacher’s Activity: Using transformer kits, a power supply, and a multimeter, the teacher demonstrates the step-up and step-down operations. The teacher shows how voltage changes when primary and secondary coils with different turns are connected.
Pupils’ Activity: Pupils observe the demonstration carefully, noting the voltage readings on the multimeter for both step-up and step-down configurations.
Learning Point: Pupils visually differentiate between step-up and step-down transformer actions.

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 types of transformer losses.
State two applications of transformers.
A transformer has 500 primary turns and 2000 secondary turns. If the primary voltage is 100V, calculate the secondary voltage.
Explain the difference 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: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the importance of transformers in electrical systems. The teacher assigns homework: “Research how transformers are used in your mobile phone charger.”
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their understanding of the lesson and are given a task to deepen their knowledge.

Lesson Keywords

Transformer – An electrical device that transfers energy between circuits with a change in voltage and current.
Efficiency – The ratio of output power to input power, indicating how well a transformer performs.
Turns Ratio – The ratio of the number of turns in the secondary coil to the primary coil.
Step-Up Transformer – Increases voltage from primary to secondary.
Step-Down Transformer – Decreases voltage from primary to secondary.
Losses – Energy dissipations such as copper loss, eddy current loss, and hysteresis loss.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex calculation problems or ask them to explain specific types of losses in detail. For pupils needing more support, the teacher will provide simplified examples, offer one-on-one guidance during practical demonstrations, and encourage peer tutoring.

Note for teachers using this lesson plan

Ensure all instructional materials, especially the transformer kits and power supply, are in good working condition before the lesson. Safety precautions should be observed when handling electrical components. Encourage active participation and questions from all pupils to ensure comprehensive understanding.