Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 2nd Term
Week: 4
Age: 16 years
Duration: 45 minutes
Subject: Basic Electricity
Curriculum Theme: Nil
Previous Lesson: AC Motors: Definition of AC Motors, Principles of Operating AC Motors and Main Features.
Topic: AC MOTOR
Subject Matter: Meaning of AC motors (recap), types of AC motors (single phase, three phase), differences between single and three phase motors (power output, efficiency).

Specific Objectives

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

Cognitive Domain:

Define an AC motor.
State the two main types of AC motors.
Explain the key differences between single-phase and three-phase AC motors.

Affective Domain:

Appreciate the importance of different AC motor types in various applications.
Value the efficiency and power output considerations when selecting an AC motor.

Psychomotor Domain:

Identify examples of appliances that use single-phase and three-phase AC motors.
Compare the characteristics of single-phase and three-phase AC motors.

Discuss with peers the applications of AC motors in daily life.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
D.N. Amu, (2018). Basic Electricity for Senior Secondary Schools. Learn Africa Publishers Plc.
https://www.electricaltechnology.org/2021/07/single-phase-vs-three-phase-motor.html
https://www.fluke.com/en-us/learn/blog/motors-drives/what-is-ac-motor

Instructional Materials

The teacher will teach this lesson with the aid of:

Motor charts showing different types of AC motors.
Appliance samples (e.g., small fan for single-phase, pictures of industrial machinery for three-phase).
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils understand the fundamental types of AC motors and their operational differences. Knowing these distinctions is important for comprehending how various electrical appliances and industrial machines function, and for making informed choices in practical applications.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of basic electrical concepts, types of current (AC and DC), and the general working principle of electric motors.

Lesson Content/Board Summary

AC Motors

Meaning of AC Motors

An AC motor is an electric motor driven by alternating current (AC). It converts electrical energy into mechanical energy, typically through the interaction of a rotating magnetic field in the stator and an electric current in the rotor.

Types of AC Motors

AC motors are broadly classified into two main types based on the number of phases in their power supply:

Single-Phase AC Motors
Three-Phase AC Motors

Single-Phase AC Motors

Single-phase AC motors operate on a single phase of alternating current. They are commonly used in residential and light commercial applications due to their simplicity and lower cost.

Characteristics:

Require a starting mechanism (e.g., capacitor, shaded pole) because a single-phase supply cannot produce a rotating magnetic field on its own.
Have lower power output compared to three-phase motors of the same size.
Less efficient for higher power applications.
Examples: Fans, refrigerators, washing machines, vacuum cleaners, pumps for domestic use.

Three-Phase AC Motors

Three-phase AC motors operate on a three-phase alternating current supply. They are widely used in industrial and heavy commercial applications because of their robustness, high efficiency, and self-starting capability.

Characteristics:

Self-starting due to the inherent rotating magnetic field produced by the three-phase supply.
Offer higher power output and torque.
More efficient than single-phase motors for the same power rating.
More robust and have a longer lifespan in heavy-duty applications.
Examples: Industrial pumps, compressors, conveyors, heavy machinery, elevators.

Differences between Single-Phase and Three-Phase AC Motors

The following are key differences between single-phase and three-phase AC motors:

Power Supply: Single-phase motors use a single-phase AC supply, while three-phase motors use a three-phase AC supply.
Starting Torque: Single-phase motors require auxiliary starting methods (e.g., capacitors) to produce starting torque, whereas three-phase motors are self-starting and produce a rotating magnetic field naturally.
Power Output: Three-phase motors generally have higher power output and torque for a given frame size compared to single-phase motors.
Efficiency: Three-phase motors are typically more efficient and have a higher power factor than single-phase motors, especially at higher loads.
Cost: Single-phase motors are generally less expensive to purchase and install for low-power applications. Three-phase motors and their associated wiring can be more expensive, but offer better value for high-power industrial uses.
Applications: Single-phase motors are used in domestic and light commercial appliances (fans, refrigerators). Three-phase motors are used in heavy industrial machinery (pumps, compressors, lifts).

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 electric motors and AC supply.
Pupils’ Activity: Pupils respond to the teacher’s questions, recalling previous knowledge.
Learning Point: Pupils connect the new lesson to their prior knowledge about motors and AC electricity.

Step 2: Meaning of AC Motors (Recap)

Time: 7 minutes
Teaching Skill: Explanation/Recall
Teacher’s Activity: The teacher defines an AC motor and explains its basic function, using the motor chart as a visual aid.
Pupils’ Activity: Pupils listen attentively and answer questions regarding the definition and function of AC motors.
Learning Point: Pupils recap the meaning and purpose of AC motors.

Step 3: Types of AC Motors

Time: 8 minutes
Teaching Skill: Listing/Classification
Teacher’s Activity: The teacher introduces the two main types of AC motors: single-phase and three-phase, listing them on the board.
Pupils’ Activity: Pupils identify the two main types of AC motors and note them down.
Learning Point: Pupils learn the broad classification of AC motors.

Step 4: Single-Phase AC Motors

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the characteristics of single-phase AC motors, including their need for starting mechanisms and typical applications, showing appliance samples or pictures.
Pupils’ Activity: Pupils listen, ask questions, and identify appliances that use single-phase motors.
Learning Point: Pupils understand the features and uses of single-phase AC motors.

Step 5: Three-Phase AC Motors

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the characteristics of three-phase AC motors, highlighting their self-starting nature, higher power, and industrial applications, using charts or pictures of industrial machines.
Pupils’ Activity: Pupils listen, ask questions, and identify typical applications of three-phase motors.
Learning Point: Pupils understand the features and uses of three-phase AC motors.

Step 6: Differences between Single-Phase and Three-Phase AC Motors

Time: 8 minutes
Teaching Skill: Comparative Analysis
Teacher’s Activity: The teacher explains and compares the key differences between single-phase and three-phase motors, focusing on power output, efficiency, starting method, and applications. The teacher writes these differences on the board.
Pupils’ Activity: Pupils listen, ask questions for clarification, and note down the comparative points.
Learning Point: Pupils can differentiate between single-phase and three-phase AC motors based on various characteristics.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

What is an AC motor?
Mention the two main types of AC motors.
State two characteristics of a single-phase AC motor.
List three differences between single-phase and three-phase AC motors.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the lesson and gives homework: “Research and list three advantages of three-phase motors over single-phase motors in industrial settings.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their understanding of AC motors and their types.

Lesson Keywords

AC Motor – An electric motor powered by alternating current.
Single-Phase Motor – An AC motor that operates on a single-phase alternating current supply.
Three-Phase Motor – An AC motor that operates on a three-phase alternating current supply.
Stator – The stationary part of a motor that contains windings.
Rotor – The rotating part of a motor.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research specific applications or internal components of different AC motor types. For pupils needing more support, the teacher can provide simplified diagrams and focus on the fundamental definitions and key differences, offering additional examples and one-on-one guidance.

Note for teachers using this lesson plan

Ensure that the motor charts are clear and easily visible to all pupils. When discussing differences, encourage pupils to think about where they might encounter these motors in their daily lives to make the lesson more relatable. Emphasize safety precautions when discussing real-world electrical appliances.