Lesson Note on Transformers: Power Transmission and Induction Coil for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Electricity and Magnetism
Previous Lesson: Electromagnetic Induction.
Topic: ELECTROMAGNETIC FIELD
Subject Matter: Transformer (principle and basic parts), power transmission (step-up and step-down idea), induction coil (meaning and use)

Specific Objectives

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

Cognitive Domain:

• Define a transformer and an induction coil.
• State the principle of operation for both transformers and induction coils.
• Identify the basic parts of a transformer and an induction coil.
• Differentiate between step-up and step-down transformers.
• Explain the role of transformers in power transmission.

Affective Domain:

• Appreciate the importance of transformers and induction coils in modern technology.
• Develop an interest in the applications of electromagnetic induction.

Psychomotor Domain:

• Draw simple, labelled diagrams of a transformer.
• Solve simple problems involving transformer ratios (voltage, turns, current).

Social Domain:

• Discuss the benefits of efficient power transmission to society.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• New School Physics by P.N. Okeke and M.W. Anyakoha

Instructional Materials

The teacher will teach this lesson with the aid of:

• Charts showing diagrams of step-up and step-down transformers
• A diagram of an induction coil
• A simple model of a transformer (if available)

Rationale for the Lesson

This lesson helps pupils understand how transformers and induction coils work, which are important devices in everyday electrical systems. It also explains how electricity is efficiently transmitted over long distances to homes and industries.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of magnetic fields, electromagnetic induction, Faraday’s law, and Lenz’s law.

Lesson Content/Board Summary

ELECTROMAGNETIC FIELD

Transformer

A transformer is an electrical device that changes the voltage of an alternating current (AC) without changing its frequency. It works on the principle of mutual induction.

Principle of Operation: When an alternating current flows through the primary coil, it creates a continuously changing magnetic flux in the soft iron core. This changing magnetic flux links with the secondary coil, inducing an electromotive force (e.m.f.) in it.

Basic Parts of a Transformer:

• Primary Coil: The coil connected to the AC input voltage.
• Secondary Coil: The coil from which the output voltage is obtained.
• Soft Iron Core: A laminated core that concentrates and guides the magnetic flux from the primary to the secondary coil, increasing efficiency.

Types of Transformers:

• Step-up Transformer: This transformer increases the AC voltage (output voltage is higher than input voltage) and decreases the current. It has more turns in the secondary coil (Ns) than in the primary coil (Np), i.e., Ns > Np.
• Step-down Transformer: This transformer decreases the AC voltage (output voltage is lower than input voltage) and increases the current. It has fewer turns in the secondary coil (Ns) than in the primary coil (Np), i.e., Ns < Np.

Transformer Equation (for an ideal transformer):

Vp / Vs = Np / Ns = Is / Ip

• Vp: Primary voltage (input voltage)
• Vs: Secondary voltage (output voltage)
• Np: Number of turns in the primary coil
• Ns: Number of turns in the secondary coil
• Ip: Primary current (input current)
• Is: Secondary current (output current)

Example 1: A step-down transformer has 1000 turns in its primary coil and 100 turns in its secondary coil. If the primary voltage is 240 V, calculate the secondary voltage.

Step 1: Identify given values.

Np = 1000 turns

Ns = 100 turns

Vp = 240 V

Vs = ?

Step 2: Use the transformer equation relating voltage and turns.

Vp / Vs = Np / Ns

240 / Vs = 1000 / 100

240 / Vs = 10

Step 3: Solve for Vs.

Vs = 240 / 10 = 24 V

The secondary voltage is 24 V.

Power Transmission

Transformers are essential for efficient power transmission over long distances.

• Step-up transformers are used at power generating stations to increase the voltage to very high levels (e.g., 132 kV, 330 kV) and reduce the current. This minimizes power loss (P = I²R) as heat in the transmission cables.
• Step-down transformers are used near consumption areas to reduce the high voltage to safer, usable levels (e.g., 33 kV, 11 kV, 415 V, 230 V) for industrial, commercial, and domestic use.

Induction Coil

An induction coil is an electrical device that generates high-voltage pulses from a low-voltage direct current (DC) supply.

Principle of Operation: It uses electromagnetic induction to produce a very rapid change in magnetic flux, which induces a high e.m.f. in the secondary coil.

Basic Parts of an Induction Coil:

• Primary Coil: Few turns of thick wire connected to a low DC voltage.
• Secondary Coil: Many turns of fine wire.
• Soft Iron Core: Concentrates magnetic flux.
• Interrupter (or contact breaker): Rapidly makes and breaks the primary circuit, causing a sudden change in magnetic flux.
• Capacitor: Connected across the interrupter contacts to reduce sparking and increase the rate of collapse of the magnetic field.

Uses of Induction Coils:

• Car ignition systems (to produce sparks for combustion).
• X-ray machines.
• Gas discharge tubes.
• Spark plugs.
• Burglar alarms.

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 learned about electromagnetic induction and its applications.
Pupils’ Activity: Pupils respond by mentioning concepts like induced current and magnetic fields.
Learning Point: Pupils recall prior knowledge related to the lesson.

Step 2: Explanation of Transformer Principle and Parts

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines a transformer, explains its principle of operation (mutual induction), and identifies its basic parts using a diagram or chart.
Pupils’ Activity: Pupils listen attentively, observe the diagrams, and ask questions for clarification.
Learning Point: Pupils understand the definition, principle, and components of a transformer.

Step 3: Types of Transformers and Power Transmission

Time: 10 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the difference between step-up and step-down transformers, including their turns ratios. The teacher then discusses their crucial role in efficient power transmission.
Pupils’ Activity: Pupils take notes and participate in a short discussion on why high voltage is used for power transmission.
Learning Point: Pupils can differentiate transformer types and understand their use in power transmission.

Step 4: Transformer Calculations (Example)

Time: 5 minutes
Teaching Skill: Problem Solving
Teacher’s Activity: The teacher works through a simple example problem involving transformer ratios (voltage and turns) on the board.
Pupils’ Activity: Pupils copy the example into their notes and attempt to solve similar problems.
Learning Point: Pupils learn to apply the transformer equation to solve basic problems.

Step 5: Explanation of Induction Coil

Time: 7 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher defines an induction coil, explains its principle of operation, and discusses its basic parts using a diagram.
Pupils’ Activity: Pupils listen and observe the diagram, noting the key features of an induction coil.
Learning Point: Pupils understand the meaning, principle, and parts of an induction coil.

Step 6: Applications of Induction Coil

Time: 3 minutes
Teaching Skill: Listing/Discussion
Teacher’s Activity: The teacher lists and briefly explains some practical applications of the induction coil in various fields.
Pupils’ Activity: Pupils note down the applications and consider their importance.
Learning Point: Pupils identify various uses of induction coils in real-life scenarios.

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. What is a transformer and what is its principle of operation?
2. Distinguish between a step-up and a step-down transformer.
3. State three basic parts of a transformer.
4. Explain why transformers are important in power transmission.
5. Define an induction coil and mention two of its uses.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 0 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson and assigns homework, which includes drawing and labeling a simple transformer diagram.
Pupils’ Activity: Pupils listen to the summary and note down the homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

• Transformer – An electrical device that changes the voltage of an alternating current.
• Mutual Induction – The process by which a changing magnetic field in one coil induces an e.m.f. in an adjacent coil.
• Step-up Transformer – Increases voltage, decreases current.
• Step-down Transformer – Decreases voltage, increases current.
• Power Transmission – The movement of electricity from a generating site to an electrical substation.
• Induction Coil – A device for generating high-voltage pulses from a low-voltage DC supply.

Differentiation

For struggling learners, the teacher will provide simplified diagrams and focus on the definitions and basic principles before moving to more complex concepts. Advanced learners will be encouraged to research and present on the efficiency of transformers and the causes of energy loss.

Note for teachers using this lesson plan

Ensure that pupils clearly understand the difference between AC and DC current when discussing transformer and induction coil operations. Emphasize the practical applications to make the topic relatable. Encourage pupils to draw diagrams neatly and accurately.