JSS3 Basic Technology Lesson Note on Scale and Its Uses

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SUB-TOPIC FOUR

(a) Scale and its uses

(b) Construction of scale: (i) Plain scale (ii) diagonal scale.

SCALE AND ITS USES

Scales are used for enlargement and reduction. A scale is used when an object is too large or too small to be recognized on paper.

Scales are represented in various ways such as:

• Percentages: 50%, 25%, 20%, 10%, 2%, 1% etc.
• Ratio: 1:2, 1:10, 1:100, 1:1000, 4:1, 3:1, 2:1 etc.
• Description: Full size, Half size, twice full size, etc.
• Representative fraction: ½, 1/10, 1/100, 1/1000 etc.

This representative fraction implies:

There are two types of Scales:

• The plain scale and
• The diagonal scale

EVALUATION:

• What is scale used for?
• Mention two types of scale
• How are scales represented?

Sub-Topic 2: Construction of scale

Construction of plain scale

Activity 1:        To construct a plain scale of 1:40mm to read up to 4meters

Procedure:

• Construct a rectangle whose length is 40mm * 4mm = 160mm.
• Divide the rectangle into 4 equal parts.
• Use the numbering as shown.
• Divide OA into 10 equal parts.
• This is a plain scale.

Activity 1:  To construct a plain scale of 1:50mm to read up to 3meters and to indicate the distance 2.6m.

Procedure:

• Construct a rectangle whose length is 50mm * 3mm = 160mm.
• Divide the rectangle into 3 equal parts.
• Number the division as shown.
• Divide OA into 10 equal parts.
• Indicate the given distance 2.6m as shown.

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