Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: Second Term
Week: 2
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Pressure And Its Measurement: Concept of Pressure and Units.
Topic: Pressure and its measurement Different types of pressure measuring devices
Subject Matter: Pressure measuring devices, barometer, manometer, applications

Specific Objectives

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

Cognitive Domain:

Define pressure and state its units.
Identify different types of pressure measuring devices.
Explain the working principles of a barometer and a manometer.

Affective Domain:

Appreciate the importance of accurate pressure measurement in refrigeration and air conditioning.
Show interest in learning about various pressure measuring instruments.

Psychomotor Domain:

Identify and name the parts of a barometer and a manometer.
State common applications of pressure measuring devices.

Work cooperatively with peers to identify and discuss pressure measuring devices.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Education Curriculum for Trade Subjects.
State Unified Scheme of Work for Senior Secondary School.
Refrigeration and Air Conditioning Technology by Billy C. Langley.

Instructional Materials

The teacher will teach this lesson with the aid of:

A barometer.
A U-tube manometer.
A pressure hose.
A pressure gauge.
Charts showing different types of pressure measuring devices.

Rationale for the Lesson

Understanding pressure and how to measure it is important for pupils in refrigeration and air conditioning. This knowledge helps them maintain, troubleshoot, and safely operate AC and refrigeration systems, preventing damage and ensuring efficiency.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of force, area, and states of matter from their previous science classes.

Lesson Content/Board Summary

Pressure and its Measurement

Definition of Pressure

Pressure is defined as the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

Mathematically, Pressure (P) = Force (F) / Area (A).

Units of Pressure

The standard international (SI) unit for pressure is the Pascal (Pa), which is Newton per square meter (N/m²).

Other common units of pressure include:

Pounds per Square Inch (PSI)
Bar
Atmosphere (atm)
Millimeters of Mercury (mmHg)
Inches of Water (inH₂O)

Types of Pressure Measuring Devices

Various devices are used to measure pressure, depending on the type and range of pressure. The main types include:

Barometers
Manometers
Pressure Gauges (e.g., Bourdon tube gauges, diaphragm gauges)

Barometer

A barometer is a scientific instrument used to measure atmospheric pressure. Atmospheric pressure is the pressure exerted by the weight of the air in the atmosphere.

Working Principle: A common type, the mercury barometer, works by balancing the mercury in a sealed tube against the atmospheric pressure. The height of the mercury column indicates the pressure.

Applications:

Weather forecasting (changes in atmospheric pressure indicate weather changes).
Aviation (for altimeters, which measure altitude based on pressure).
Scientific research.

Manometer

A manometer is a device used to measure the pressure of fluids (liquids or gases) in a confined space, often relative to atmospheric pressure or another pressure source.

Types of Manometers:

U-tube Manometer: A simple U-shaped tube containing a liquid (like mercury or water). The difference in liquid levels in the two arms indicates the pressure difference.
Well-type Manometer: Similar to a U-tube but with one arm having a much larger diameter (a well), making readings easier.

Working Principle: Manometers operate on the principle that the pressure difference between two points is proportional to the difference in height of the liquid column in the tube.

Applications in Refrigeration and Air Conditioning:

Measuring refrigerant pressures in systems.
Checking pressure drops across filters or coils.
Detecting leaks in systems.
Balancing airflow in duct systems.

Pressure Gauges

Pressure gauges are mechanical or electronic devices used to measure and display pressure in various industrial and domestic applications. They are commonly used for measuring absolute, gauge, and differential pressures.

Example: Bourdon tube pressure gauges are widely used in refrigeration and air conditioning to show the pressure inside refrigerant lines and equipment.

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, reviews the previous lesson briefly, and then asks pupils about their understanding of “force” and “area” to introduce the concept of pressure.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils recall prior knowledge and are prepared for the new topic.

Step 2: Definition and Units of Pressure

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines pressure as force per unit area, writes the formula on the board, and lists common units of pressure like Pascal and PSI. The teacher explains the significance of knowing these units.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and standard units of pressure.

Step 3: Introduction to Pressure Measuring Devices

Time: 5 minutes
Teaching Skill: Listing/Categorization
Teacher’s Activity: The teacher introduces the idea that pressure needs to be measured and lists the main types of devices used for this, such as barometers, manometers, and pressure gauges.
Pupils’ Activity: Pupils listen and identify the different categories of devices.
Learning Point: Pupils are introduced to the variety of instruments for measuring pressure.

Step 4: The Barometer

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains what a barometer is and its purpose (measuring atmospheric pressure). Using a chart or an actual barometer (if available), the teacher explains its working principle and mentions its applications, especially in weather forecasting.
Pupils’ Activity: Pupils observe the barometer or chart, listen to the explanation, and ask questions about its operation.
Learning Point: Pupils understand what a barometer is, how it works, and its uses.

Step 5: The Manometer

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains what a manometer is and how it measures fluid pressure. The teacher focuses on the U-tube manometer, explaining its construction and working principle using a diagram or a physical model. The teacher highlights its applications in refrigeration and air conditioning.
Pupils’ Activity: Pupils observe the manometer or diagram, listen to the explanation, and note down the applications.
Learning Point: Pupils understand the manometer, its types, working principle, and relevance to their trade.

Step 6: Other Pressure Gauges and Applications

Time: 5 minutes
Teaching Skill: Elaboration/Application
Teacher’s Activity: The teacher briefly discusses other common pressure gauges, such as the Bourdon tube gauge, and reinforces the general importance of accurate pressure measurement in maintaining and troubleshooting refrigeration and AC systems.
Pupils’ Activity: Pupils listen and connect the learned concepts to practical applications.
Learning Point: Pupils broaden their knowledge of pressure measuring devices and their practical relevance.

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 pressure and state its SI unit.
Mention two types of pressure measuring devices.
Explain the main purpose of a barometer.
List two applications of a manometer in refrigeration and air conditioning.

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, emphasizing the importance of accurate pressure measurement in their chosen trade. The teacher then gives an assignment: “Research and draw a labeled diagram of a Bourdon tube pressure gauge.”
Pupils’ Activity: Pupils listen to the summary and copy the assignment.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Pressure – Force applied perpendicular to a surface per unit area.
Pascal (Pa) – The SI unit of pressure.
Barometer – An instrument used to measure atmospheric pressure.
Manometer – A device used to measure the pressure of fluids in a confined space.
Atmospheric Pressure – The pressure exerted by the weight of the air in the atmosphere.
PSI – Pounds per Square Inch, another common unit of pressure.

Differentiation

For visual learners, the teacher will use charts, diagrams, and actual devices for demonstration. Auditory learners will benefit from the teacher’s explanations and class discussions. Kinesthetic learners will be encouraged to handle the available instruments safely and identify their parts. Pupils needing additional support will be paired with stronger peers for discussion and clarification, while advanced learners can research more complex pressure measurement techniques.

Note for teachers using this lesson plan

Teachers should ensure that actual pressure measuring devices are available for demonstration to enhance practical understanding. Emphasize safety precautions when handling pressure equipment. Encourage pupils to relate the concepts directly to practical scenarios they might encounter in refrigeration and air conditioning systems. Adjust the pace of the lesson based on pupils’ engagement and prior knowledge.