Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: Second Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Pressure And Its Measurement: Types of Pressure Measuring Devices and Uses.
Topic: Pressure and its measurement: Barometer and Manometers as pressure measuring devices
Subject Matter: Barometer operation, manometer operation, reading pressure values

Specific Objectives

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

Cognitive Domain:

Define pressure and atmospheric pressure.
Describe the principle of operation of a mercury barometer.
Explain the principle of operation of a U-tube manometer.
State how to read pressure values from a barometer and a manometer.

Affective Domain:

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

Psychomotor Domain:

Identify the main parts of a mercury barometer and a U-tube manometer.
Demonstrate how to read pressure values from a mercury barometer.
Demonstrate how to read pressure values from a U-tube manometer.

Work collaboratively in groups to interpret pressure readings from diagrams of measuring devices.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum
State Unified Scheme of Work
Refrigeration and Air Conditioning Technology Textbook

Instructional Materials

The teacher will teach this lesson with the aid of:

A mercury barometer
A U-tube manometer
A ruler scale
A stand
Whiteboard/Blackboard and marker
Charts illustrating the operation of barometers and manometers

Rationale for the Lesson

Understanding pressure and its measurement is important for pupils in refrigeration and air conditioning as it helps them comprehend how systems operate. This knowledge is essential for diagnosing faults and ensuring the efficient functioning of cooling systems, which they will encounter in their future careers.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of force, area, and the general concept of pressure.

Lesson Content/Board Summary

Pressure and its Measurement

Definition of Pressure

Pressure is defined as force applied perpendicular to the surface of an object per unit area over which the force is distributed. The SI unit for pressure is the Pascal (Pa).

Atmospheric pressure is the pressure exerted by the weight of the air in the atmosphere.

Barometer Operation

A barometer is an instrument used to measure atmospheric pressure. A mercury barometer consists of an inverted glass tube sealed at one end and open at the other, placed in a reservoir of mercury.

The principle of operation for a mercury barometer:

Atmospheric pressure acting on the surface of the mercury in the reservoir supports a column of mercury in the inverted tube.
The height of this mercury column indicates the atmospheric pressure.

To read pressure values from a mercury barometer:

Observe the height of the mercury column from the surface in the reservoir to the top of the column.
Use a scale attached to the barometer to read this height, usually in millimeters of mercury (mmHg) or inches of mercury (inHg).

Manometer Operation

A manometer is a device used to measure differences in pressure, especially in fluids. A U-tube manometer is a common type, consisting of a U-shaped tube containing a liquid (often mercury or water).

The principle of operation for a U-tube manometer:

When both ends of the U-tube are open to the atmosphere, the liquid levels in both arms are equal.
When one end is connected to a pressure source, the difference in liquid levels in the two arms indicates the pressure difference.

To read pressure values from a U-tube manometer:

Measure the difference in height (h) between the liquid levels in the two arms of the U-tube using a ruler scale.
This height difference directly corresponds to the gauge pressure or pressure difference, often expressed in mm of liquid (e.g., mmH2O or mmHg).
If one end is open to the atmosphere, the reading gives gauge pressure.

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 asks pupils if they know what makes a car tyre hard or a balloon inflate. The teacher then introduces the topic: Pressure and its measurement.
Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction of the new topic.
Learning Point: Pupils are prepared for the lesson and connect previous knowledge to the new topic.

Step 2: Definition of Pressure

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines pressure, atmospheric pressure, and mentions common units of pressure. The teacher writes key definitions on the board.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the fundamental definition of pressure.

Step 3: Barometer Operation

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher displays a mercury barometer or a chart illustrating it. The teacher explains its parts and demonstrates its principle of operation, showing how atmospheric pressure supports the mercury column.
Pupils’ Activity: Pupils observe the barometer or chart, listen to the explanation, and identify its parts.
Learning Point: Pupils understand how a barometer works to measure atmospheric pressure.

Step 4: Reading Barometer Values

Time: 5 minutes
Teaching Skill: Practical Application
Teacher’s Activity: The teacher guides pupils on how to correctly read the atmospheric pressure from the barometer scale, emphasizing the importance of reading at eye level.
Pupils’ Activity: Pupils practice reading values from the barometer or a clear diagram provided.
Learning Point: Pupils can accurately read atmospheric pressure values.

Step 5: Manometer Operation

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher displays a U-tube manometer or a chart illustrating it. The teacher explains its parts and demonstrates its principle of operation, showing how pressure difference affects the liquid levels.
Pupils’ Activity: Pupils observe the manometer or chart, listen to the explanation, and identify its parts.
Learning Point: Pupils understand how a manometer works to measure pressure differences.

Step 6: Reading Manometer Values

Time: 5 minutes
Teaching Skill: Practical Application
Teacher’s Activity: The teacher guides pupils on how to correctly read the pressure difference from the manometer scale, emphasizing the measurement of the height difference.
Pupils’ Activity: Pupils practice reading values from the manometer or a clear diagram provided.
Learning Point: Pupils can accurately read pressure values using a manometer.

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.
What is a barometer used for?
Explain the principle of operation of a mercury barometer.
How do you determine the pressure reading from a U-tube manometer?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: Remaining minutes
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the importance of accurate pressure measurement in refrigeration and air conditioning. The teacher assigns homework which includes drawing and labeling a barometer and a manometer.
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their understanding of the lesson and prepare for further study.

Lesson Keywords

Pressure – Force applied perpendicular to a surface per unit area.
Barometer – An instrument used to measure atmospheric pressure.
Manometer – A device used to measure pressure differences or gauge pressure.
Atmospheric Pressure – The pressure exerted by the weight of the air in the atmosphere.
Mercury Column – The column of mercury in a barometer or manometer, whose height indicates pressure.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional scenarios for interpreting pressure readings or ask them to research other types of pressure gauges. For pupils needing more support, the teacher will provide one-on-one guidance, use simplified diagrams, and encourage peer learning within small groups.

Note for teachers using this lesson plan

Ensure that actual barometers and manometers are available for demonstration. If not, clear, large diagrams or videos should be used to illustrate the operation of these devices. Emphasize safety precautions if using mercury-based instruments. Encourage pupils to actively participate in reading and interpreting the values.