Lesson Note on Electromagnetic Field: Motors and Moving Coil Galvanometer for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 8
Age: 16 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Electromagnetic Phenomena
Previous Lesson: Earth’s Magnetic Field: Declination, Dip and Compass Use.
Topic: ELECTROMAGNETIC FIELD
Subject Matter: Magnetic force on a charge moving in a magnetic field (Lorentz force idea), concept of electromagnetic field (combined fields), interaction between magnetic field and currents (current-carrying wire in magnetic field, current-carrying solenoid in magnetic field), applications of electromagnetic field (electric motor, moving coil galvanometer)

Specific Objectives

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

Cognitive Domain:

• Define Lorentz force and electromagnetic field.
• State the formula for magnetic force on a moving charge and a current-carrying conductor.
• Explain the principle of operation of an electric motor and a moving coil galvanometer.

Affective Domain:

• Appreciate the importance of electromagnetic fields in modern technology.
• Develop interest in the practical applications of electromagnetism.

Psychomotor Domain:

• Apply Fleming’s Left-Hand Rule to determine the direction of magnetic force.
• Draw simple diagrams of an electric motor and a moving coil galvanometer.
• Observe and describe the effect of current in a solenoid.

Social Domain:

• Collaborate with peers to discuss the concepts and applications of electromagnetism.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• Any recommended Physics textbook for Senior Secondary Schools (e.g., New School Physics by P.N. Okeke)

Instructional Materials

The teacher will teach this lesson with the aid of:

• Physics textbook
• Charts showing diagrams of electric motor and moving coil galvanometer
• Equipped laboratory with power supply, connecting wires, solenoid, bar magnet, ammeter
• Model of an electric motor and a moving coil galvanometer

Rationale for the Lesson

This lesson helps pupils understand how electricity and magnetism are interconnected, forming electromagnetic fields. It enables pupils to grasp the fundamental principles behind many common electrical devices, which is important for understanding modern technology.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of electric current, magnetic fields around conductors, and basic principles of magnetism.

Lesson Content/Board Summary

ELECTROMAGNETIC FIELD

1. Magnetic Force on a Charge Moving in a Magnetic Field (Lorentz Force)

The Lorentz force is the force experienced by a charged particle moving through a magnetic field.

The magnitude of this force is given by the formula:

F = qvBsinθ

• F = Magnetic force (measured in Newtons, N)
• q = Magnitude of the charge (measured in Coulombs, C)
• v = Velocity of the charge (measured in meters per second, m/s)
• B = Magnetic field strength or magnetic flux density (measured in Tesla, T)
• θ = Angle between the velocity vector (v) and the magnetic field vector (B)

The direction of the force is given by Fleming’s Left-Hand Rule.

Worked Example 1:

An electron (charge = 1.6 x 10^-19 C) moves at a speed of 3 x 10⁶ m/s perpendicularly into a uniform magnetic field of 0.4 T. Calculate the magnetic force on the electron.

Step 1: Identify given values and formula.
q = 1.6 x 10^-19 C
v = 3 x 10⁶ m/s
B = 0.4 T
θ = 90° (since it moves perpendicularly), so sin 90° = 1
Formula: F = qvBsinθ

Step 2: Substitute values into the formula.
F = (1.6 x 10^-19 C) x (3 x 10⁶ m/s) x (0.4 T) x 1

Step 3: Calculate and state the unit.
F = 1.92 x 10^-13 N

2. Concept of Electromagnetic Field

An electromagnetic field is a physical field produced by electrically charged objects. It consists of both electric and magnetic fields, which are interconnected and can produce each other.

3. Interaction Between Magnetic Field and Currents

a. Current-Carrying Wire in a Magnetic Field

A current-carrying conductor placed in a magnetic field experiences a force. This is known as the motor effect.

The magnitude of this force is given by the formula:

F = BILsinθ

• F = Magnetic force (measured in Newtons, N)
• B = Magnetic field strength (measured in Tesla, T)
• I = Current in the conductor (measured in Amperes, A)
• L = Length of the conductor in the magnetic field (measured in meters, m)
• θ = Angle between the direction of current (I) and the magnetic field (B)

The direction of the force is determined by Fleming’s Left-Hand Rule.

Worked Example 2:

A straight wire carrying a current of 5 A is placed in a uniform magnetic field of 0.8 T. If the length of the wire in the field is 0.2 m and it is perpendicular to the field, calculate the force experienced by the wire.

Step 1: Identify given values and formula.
I = 5 A
B = 0.8 T
L = 0.2 m
θ = 90° (perpendicular), so sin 90° = 1
Formula: F = BILsinθ

Step 2: Substitute values into the formula.
F = (0.8 T) x (5 A) x (0.2 m) x 1

Step 3: Calculate and state the unit.
F = 0.8 N

b. Current-Carrying Solenoid in a Magnetic Field

When current passes through a solenoid, it acts as an electromagnet, producing its own magnetic field. When this solenoid is placed in an external magnetic field, the two fields interact. This interaction can cause the solenoid to move or rotate, depending on its orientation and the direction of the fields.

4. Applications of Electromagnetic Field

a. Electric Motor

An electric motor converts electrical energy into mechanical energy. Its operation is based on the motor effect, where a current-carrying coil placed in a magnetic field experiences a turning force (torque).

• Principle: Motor effect (force on a current-carrying conductor in a magnetic field).
• Key parts: Armature (coil), field magnets, commutator, carbon brushes.
• Working idea: Current flows through the coil, creating a magnetic field that interacts with the permanent magnetic field, causing the coil to rotate continuously.

b. Moving Coil Galvanometer

A moving coil galvanometer is a sensitive instrument used to detect and measure small electric currents. It works on the principle that a current-carrying coil placed in a magnetic field experiences a torque, causing it to deflect.

• Principle: Motor effect (deflection of a coil proportional to the current flowing through it).
• Key parts: Coil, permanent magnets, soft iron core, spring, pointer, scale.
• Working idea: When current passes through the coil, it experiences a torque in the magnetic field, causing it to rotate. The rotation is opposed by a spring, and the deflection of the pointer is proportional to the current.

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 asks pupils to recall what they know about magnetic fields and how they are produced. The teacher then introduces the topic of electromagnetic fields and their importance.
Pupils’ Activity: Pupils respond to questions about magnetic fields and listen attentively to the introduction.
Learning Point: Pupils connect previous knowledge to the new topic and understand the relevance of electromagnetic fields.

Step 2: Magnetic Force on a Moving Charge (Lorentz Force)

Time: 7 minutes
Teaching Skill: Explanation/Derivation
Teacher’s Activity: The teacher explains the concept of Lorentz force, defines it, states the formula F = qvBsinθ, explains each variable, and provides a worked example.
Pupils’ Activity: Pupils listen, take notes, ask questions for clarity, and solve the example problem.
Learning Point: Pupils understand the force experienced by a moving charge in a magnetic field and can apply the formula.

Step 3: Electromagnetic Field and Force on Current-Carrying Wire

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines an electromagnetic field. The teacher then explains the force on a current-carrying wire in a magnetic field (motor effect), states the formula F = BILsinθ, explains variables, and demonstrates Fleming’s Left-Hand Rule.
Pupils’ Activity: Pupils listen, observe the demonstration, and practice applying Fleming’s Left-Hand Rule.
Learning Point: Pupils understand how an electromagnetic field is formed and the force experienced by a current-carrying wire in a magnetic field.

Step 4: Current-Carrying Solenoid in a Magnetic Field

Time: 7 minutes
Teaching Skill: Practical Demonstration/Observation
Teacher’s Activity: The teacher sets up a simple experiment with a solenoid and a magnet, passing current through the solenoid, and guides pupils to observe the interaction and record their observations.
Pupils’ Activity: Pupils observe the experiment, describe what happens when current passes through the solenoid in the presence of a magnetic field, and discuss their findings.
Learning Point: Pupils understand that a current-carrying solenoid behaves like a magnet and interacts with other magnetic fields.

Step 5: Applications – Electric Motor

Time: 7 minutes
Teaching Skill: Explanation/Visual Aid
Teacher’s Activity: The teacher explains the principle of an electric motor using a chart or model, highlighting its key parts and explaining how it converts electrical energy to mechanical energy.
Pupils’ Activity: Pupils observe the charts/model, listen to the explanation, and ask questions about the motor’s operation.
Learning Point: Pupils understand the working principle and basic components of an electric motor.

Step 6: Applications – Moving Coil Galvanometer

Time: 4 minutes
Teaching Skill: Explanation/Visual Aid
Teacher’s Activity: The teacher explains the principle of a moving coil galvanometer using a chart or model, explaining how it detects and measures current.
Pupils’ Activity: Pupils observe the charts/model, listen to the explanation, and understand how a galvanometer works.
Learning Point: Pupils understand the working principle and basic components of a moving coil galvanometer.

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. Define Lorentz force.
2. State the formula for the magnetic force on a charge moving in a magnetic field, explaining all symbols.
3. What is an electromagnetic field?
4. Explain the principle of operation of an electric motor.
5. Mention two applications of electromagnetic fields.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teacher’s Activity: The teacher summarizes the key points of the lesson and assigns homework, which includes drawing simple diagrams of an electric motor and a moving coil galvanometer.
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their understanding and prepare for further study.

Lesson Keywords

• Lorentz force – The force experienced by a charged particle moving in a magnetic field.
• Electromagnetic field – A field consisting of both electric and magnetic components, produced by charged objects.
• Solenoid – A coil of wire acting as a magnet when current passes through it.
• Electric motor – A device that converts electrical energy into mechanical energy.
• Moving coil galvanometer – An instrument used to detect and measure small electric currents.
• Fleming’s Left-Hand Rule – A rule used to determine the direction of force on a current-carrying conductor in a magnetic field.

Differentiation

For struggling learners, the teacher will provide simplified diagrams and focus on the definitions and basic principles. For advanced learners, the teacher will encourage them to research more complex applications of electromagnetic fields, such as electromagnetic induction or magnetic levitation, and to solve more challenging problems involving the formulas.

Note for teachers using this lesson plan

Ensure that all practical demonstrations are conducted safely and that pupils understand the safety precautions. Emphasize the practical applications of electromagnetic fields to make the lesson more relatable. Encourage pupils to draw and label diagrams accurately, as this is important for understanding the concepts and for examinations.