Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 4
Age: 15 years
Duration: 45 minutes
Subject: Technical Drawing
Curriculum Theme: Technical Drawing
Previous Lesson: Scales: Plain and Diagonal Scales Construction and Reading.
Topic: ENLARGEMENT AND REDUCTION
Subject Matter: Concept of enlargement, concept of reduction, application of enlargement and reduction in plane figures, working with given ratios for scaling drawings.

Specific Objectives

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

Cognitive Domain:

Define enlargement and reduction in technical drawing.
State the applications of enlargement and reduction in plane figures.
Explain how to use given ratios for scaling drawings.

Affective Domain:

Appreciate the importance of accurate scaling in technical drawing.
Show interest in performing enlargement and reduction tasks.

Psychomotor Domain:

Apply the principles of enlargement to scale up a given plane figure.
Apply the principles of reduction to scale down a given plane figure.
Accurately draw scaled figures using specified ratios.

Collaborate with peers to solve scaling problems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Technical Drawing.
State Unified Scheme of Work for Technical Drawing (SSS 1).
Akinola, O. (2018). Technical Drawing for Senior Secondary Schools. Ibadan: University Press PLC.

Instructional Materials

The teacher will teach this lesson with the aid of:

Charts showing examples of enlarged and reduced figures.
Posters illustrating scaling ratios.
Models of objects scaled up or down.
Drawing instruments (ruler, set squares, compass, protractor).

Rationale for the Lesson

This lesson helps pupils understand how to change the size of drawings accurately. This skill is important for representing large objects on small papers or small objects in detail, which is useful in various technical fields and daily life applications.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of plane figures, drawing instruments, and simple ratios from their previous mathematics and technical drawing lessons.

Lesson Content/Board Summary

ENLARGEMENT AND REDUCTION

Concept of Enlargement

Enlargement is the process of increasing the size of a drawing or figure proportionally while maintaining its original shape and angles.

Examples of enlargement in daily life include:

Magnifying an image.
Creating a large map from a smaller one.
Designing large architectural plans from smaller sketches.

Concept of Reduction

Reduction is the process of decreasing the size of a drawing or figure proportionally while maintaining its original shape and angles.

Examples of reduction in daily life include:

Shrinking an image.
Drawing a large building on a small piece of paper.
Creating scale models of vehicles or buildings.

Applications of Enlargement and Reduction in Plane Figures

Enlargement and reduction are applied in various fields, including:

Architecture: To draw large buildings on standard paper sizes.
Engineering: To represent large machinery or components in drawings.
Cartography (Map Making): To show large geographical areas on a map.
Fashion Design: To scale patterns for different sizes.
Product Design: To create prototypes or models at different scales.

Working with Given Ratios for Scaling Drawings

Scaling drawings involves using a ratio to determine the new dimensions of a figure. A ratio of 1:X means the drawing is X times smaller than the actual object (reduction), while a ratio of X:1 means the drawing is X times larger than the actual object (enlargement).

Steps to scale a drawing using a ratio:

Identify the original dimensions of the figure.
Determine the scaling factor from the given ratio (e.g., for 1:2, the scaling factor is 1/2; for 2:1, the scaling factor is 2).
Multiply each original dimension by the scaling factor to get the new dimensions.
Draw the new figure using the calculated dimensions, ensuring all angles remain the same.

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 if they have ever seen a small picture made bigger, or a large object drawn on a small paper. The teacher then introduces the topic: Enlargement and Reduction.
Pupils’ Activity: Pupils respond to the questions and listen attentively.
Learning Point: Pupils are introduced to the concept of changing drawing sizes.

Step 2: Explanation of Enlargement

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines enlargement as making a figure larger proportionally. Using charts and models, the teacher demonstrates examples of enlarged figures, explaining how all dimensions increase by a constant factor while shape and angles remain the same.
Pupils’ Activity: Pupils observe the examples, ask questions, and take notes.
Learning Point: Pupils understand the concept and characteristics of enlargement.

Step 3: Explanation of Reduction

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines reduction as making a figure smaller proportionally. Using charts and models, the teacher demonstrates examples of reduced figures, explaining how all dimensions decrease by a constant factor while shape and angles remain the same.
Pupils’ Activity: Pupils observe the examples, ask questions, and take notes.
Learning Point: Pupils understand the concept and characteristics of reduction.

Step 4: Demonstrating Applications

Time: 8 minutes
Teaching Skill: Illustration/Application
Teacher’s Activity: The teacher discusses various real-world applications of enlargement and reduction, such as in architecture, engineering, and map-making, showing how these techniques are used to represent objects effectively.
Pupils’ Activity: Pupils participate in the discussion, giving their own examples of applications.
Learning Point: Pupils identify the practical relevance of enlargement and reduction.

Step 5: Working with Ratios

Time: 8 minutes
Teaching Skill: Demonstration/Problem-solving
Teacher’s Activity: The teacher explains how to use given ratios (e.g., 1:2 for reduction, 2:1 for enlargement) to scale drawings. The teacher demonstrates on the board with a simple plane figure (e.g., a rectangle) how to calculate new dimensions using a specific ratio.
Pupils’ Activity: Pupils observe the demonstration, ask clarifying questions, and copy the examples.
Learning Point: Pupils learn the method for applying ratios to scale drawings.

Step 6: Guided Practice

Time: 5 minutes
Teaching Skill: Practice/Supervision
Teacher’s Activity: The teacher gives pupils a simple figure with dimensions and a ratio (e.g., a square of 40mm side to be reduced by a ratio of 1:2) and asks them to calculate the new dimensions and sketch the scaled figure.
Pupils’ Activity: Pupils work individually or in pairs to calculate and sketch the figures.
Learning Point: Pupils practice applying scaling ratios to simple figures.

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 enlargement in technical drawing.
What is reduction, and how does it differ from enlargement?
Mention two applications of enlargement and reduction in daily life or technical fields.
If a line is 50mm long and you want to reduce it by a ratio of 1:5, what will be its new length?

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, emphasizing the importance of accurate scaling. The teacher assigns homework: Scale a given triangle with sides 30mm, 40mm, 50mm by a ratio of 2:1.
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils review the main concepts and receive an assignment for practice.

Lesson Keywords

Enlargement – The process of increasing the size of a figure proportionally.
Reduction – The process of decreasing the size of a figure proportionally.
Ratio – A comparison of two numbers used to determine the scaling factor.
Scaling – The process of changing the size of a drawing or figure while maintaining its proportions.
Plane figures – Two-dimensional shapes like squares, triangles, circles.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex figures or ask them to explore different scaling methods. For pupils needing more support, the teacher will provide additional one-on-one guidance and simpler examples, perhaps using graph paper for easier scaling.

Note for teachers using this lesson plan

Ensure that pupils have a clear understanding of ratios before attempting practical scaling exercises. Emphasize the importance of maintaining proportionality to avoid distortion of the figures. Encourage hands-on practice with drawing instruments.