Lesson Note on Magnetic Field: Meaning, Field Around Magnets and Making Magnets for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: 3rd Term
Week: 5
Age: 16 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Magnetic Phenomena
Previous Lesson: Electric Field: Capacitors, Capacitance and Energy Storage.
Topic: MAGNETIC FIELD
Subject Matter: Meaning of magnetic field (region where magnetic force acts), properties of magnet (poles and attraction), magnetic flux and flux density (basic idea), magnetic field around a bar magnet (field pattern), magnetic field around a straight conductor carrying current (field lines), magnetic field around a solenoid (electromagnet field), methods of making magnets (stroking, electrical method), methods of demagnetization (heating, hammering, AC method)

Specific Objectives

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

Cognitive Domain:

• Define a magnetic field.
• State the properties of a magnet.
• Explain magnetic flux and flux density.
• Describe the field patterns around different magnetic sources.
• List methods of making and demagnetizing magnets.

Affective Domain:

• Appreciate the importance of magnetic fields in daily life.
• Show interest in understanding magnetic phenomena.
• Demonstrate carefulness when handling magnets and electrical circuits.

Psychomotor Domain:

• Classify materials as magnetic or non-magnetic through simple tests.
• Sketch magnetic field patterns around a bar magnet and a current-carrying conductor.
• Perform simple experiments to demonstrate magnetization and demagnetization.

Social Domain:

• Collaborate with peers to discuss magnetic field concepts.
• Participate actively in classroom demonstrations and discussions.

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 S.L. Etuk

Instructional Materials

The teacher will teach this lesson with the aid of:

• Bar magnets
• Iron filings
• Plotting compasses
• Connecting wires
• Battery/power supply
• Straight conductor
• Solenoid
• Soft iron core
• Hammer
• Bunsen burner/heating source
• Ammeter
• Textbook and charts showing magnetic field patterns.

Rationale for the Lesson

This lesson helps pupils understand magnetic fields, which are fundamental to many technologies such as electric motors, generators, and data storage. Understanding these concepts enables pupils to grasp how these devices work and their applications in everyday life.

Prerequisite/Previous Knowledge

Pupils are expected to have prior knowledge of basic electricity, forces, and the concept of attraction and repulsion.

Lesson Content/Board Summary

Magnetic Field

Meaning of Magnetic Field

A magnetic field is the region or space around a magnet or a current-carrying conductor where magnetic force can be detected. It is an area where magnetic effects are noticeable.

Properties of a Magnet

The main properties of a magnet include:

• Poles: Every magnet has two poles, a North pole and a South pole. These poles always exist in pairs.
• Attraction and Repulsion: Like poles repel each other (e.g., North-North), while unlike poles attract each each other (e.g., North-South).
• Directional Property: A freely suspended magnet always rests in the North-South direction.
• Magnetic Induction: A magnet can induce magnetism in other magnetic materials placed near it.

Magnetic Flux and Flux Density

Magnetic Flux (Φ): This is a measure of the total number of magnetic field lines passing through a given area. Its unit is the Weber (Wb).

Magnetic Flux Density (B): This is the magnetic flux per unit area perpendicular to the direction of the magnetic field. It represents the strength of the magnetic field. Its unit is the Tesla (T).

The formula for magnetic flux density is:

B = Φ / A

Where:
B = Magnetic Flux Density (Tesla, T)
Φ = Magnetic Flux (Weber, Wb)
A = Area (square meters, m²)

Magnetic Field Around a Bar Magnet

The magnetic field lines around a bar magnet originate from the North pole and enter the South pole externally, forming continuous closed loops within the magnet. The field lines are denser near the poles, indicating a stronger field.

• Field lines never intersect.
• The direction of the field at any point is indicated by the direction of a small compass needle placed at that point.

Magnetic Field Around a Straight Conductor Carrying Current

When current flows through a straight conductor, a magnetic field is produced around it in concentric circles. The direction of these circular field lines can be determined using the Right-Hand Grip Rule (or Maxwell’s Corkscrew Rule): If the thumb points in the direction of the current, the curled fingers indicate the direction of the magnetic field lines.

• The strength of the field decreases as the distance from the conductor increases.
• The field strength is proportional to the current.

Magnetic Field Around a Solenoid (Electromagnet Field)

A solenoid is a coil of wire. When current passes through a solenoid, it behaves like a bar magnet, producing a magnetic field. The field lines inside a long solenoid are parallel and uniform, running from one end to the other, making it a strong and uniform magnetic field. Outside, the field pattern is similar to that of a bar magnet.

• The strength of the electromagnet depends on the number of turns in the coil, the current flowing through it, and the type of core material (e.g., soft iron core increases strength).

Methods of Making Magnets

Magnets can be made using various methods:

• Single Stroking Method: A magnetic material (e.g., steel bar) is stroked repeatedly in one direction with one pole of a strong magnet.
• Double Stroking Method: Two magnets are used to stroke a steel bar from the middle outwards towards the ends, with opposite poles touching the bar.
• Electrical Method (Electromagnetic Induction): A magnetic material is placed inside a solenoid through which a direct current (DC) is passed for a short period. This is the most effective method for making strong magnets.

Methods of Demagnetization

A magnet can lose its magnetism (demagnetization) through:

• Heating: Heating a magnet to a high temperature (above its Curie temperature) causes its domains to become disoriented, leading to demagnetization.
• Hammering/Rough Handling: Repeated hammering or dropping a magnet can disorient the magnetic domains, causing it to lose its magnetism.
• Alternating Current (AC) Method: Placing a magnet inside a solenoid carrying an alternating current (AC) and slowly withdrawing it, or gradually reducing the AC to zero, will demagnetize it. The continuously reversing field disorients the domains.

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 identify objects that attract metallic materials in the classroom. The teacher then introduces the topic “Magnetic Field” and relates it to their observations.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils are introduced to the concept of magnetism and the lesson topic.

Step 2: Explanation of Magnetic Field and Properties

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines a magnetic field and demonstrates with a bar magnet and iron filings how magnetic force acts in a region. The teacher also explains the properties of magnets, such as poles and attraction/repulsion, using two bar magnets.
Pupils’ Activity: Pupils observe the demonstration, participate by identifying magnetic regions, and note down the definitions and properties.
Learning Point: Pupils understand the meaning of a magnetic field and the basic properties of magnets.

Step 3: Introduction to Magnetic Flux and Flux Density

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the concepts of magnetic flux and magnetic flux density, stating their units and the relationship between them. The teacher writes the formula on the board.
Pupils’ Activity: Pupils listen, ask questions for clarity, and copy the definitions and formula into their notes.
Learning Point: Pupils learn about magnetic flux and flux density as measures of magnetic field.

Step 4: Demonstrating Magnetic Field Patterns

Time: 10 minutes
Teaching Skill: Demonstration/Illustration
Teacher’s Activity: The teacher uses iron filings and plotting compasses to demonstrate and sketch the magnetic field patterns around a bar magnet, a straight current-carrying conductor (using a cardboard and current setup), and briefly explains the field around a solenoid. The teacher emphasizes the direction of field lines.
Pupils’ Activity: Pupils observe the demonstrations carefully, ask questions, and attempt to sketch the patterns as guided by the teacher.
Learning Point: Pupils visualize and understand the patterns of magnetic fields around different sources.

Step 5: Methods of Making Magnets

Time: 6 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains and demonstrates the single stroking method using a magnet and a steel bar. The teacher also explains the electrical method, highlighting its effectiveness.
Pupils’ Activity: Pupils observe the demonstration and list the different methods of making magnets.
Learning Point: Pupils learn practical ways to create magnets.

Step 6: Methods of Demagnetization

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher discusses the methods of demagnetization, such as heating, hammering, and the use of alternating current (AC). The teacher explains the principles behind each method.
Pupils’ Activity: Pupils listen and note down the methods and explanations.
Learning Point: Pupils understand how magnets can lose their magnetism.

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 magnetic field?
2. State two properties of a magnet.
3. Describe the magnetic field pattern around a bar magnet.
4. Mention two methods of making a magnet.
5. List two ways a magnet can be demagnetized.

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, reiterating the importance of magnetic fields in technology and everyday life. The teacher also gives pupils an assignment to draw the field patterns discussed.
Pupils’ Activity: Pupils listen to the summary and copy the assignment.
Learning Point: Pupils consolidate their understanding and are given tasks for further practice.

Lesson Keywords

• Magnetic field – The region around a magnet where its influence can be felt.
• Magnetic poles – The regions of a magnet where the magnetic effect is strongest.
• Magnetic flux – The total number of magnetic field lines passing through an area.
• Magnetic flux density – The strength of a magnetic field, measured as flux per unit area.
• Solenoid – A coil of wire that acts as a magnet when current flows through it.
• Demagnetization – The process of causing a magnet to lose its magnetism.

Differentiation

For pupils who grasp concepts quickly, the teacher will provide more complex problems involving magnetic force on current-carrying conductors. For those who need more support, the teacher will provide simplified diagrams and offer one-on-one guidance during practical demonstrations, focusing on the basic definitions and observations.

Note for teachers using this lesson plan

Ensure all demonstration materials are readily available and in good working condition before the lesson. Emphasize safety precautions, especially when dealing with electrical circuits. Encourage pupils to actively participate in discussions and practical activities to foster a deeper understanding of magnetic fields.