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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:Â Â Â Â Â Â Â 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:Â 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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