Activity 30
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OBJECTIVE
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MATERIAL REQUIRED
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To find a formula for the curved surface
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Coloured chart paper, cellotape,
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area of a
right circular cylinder,
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ruler.
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experimentally.
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METHOD OF CONSTRUCTION
1. Take a
rectangular chart paper of length l units and
breadth b units [see Fig. 1].
Fold this paper along its breadth and join the two ends
by using cellotape and obtain a cylinder as shown in Fig. 2.
DEMONSTRATION
1.
Length of the rectangular paper = l = circumference of
the base of the cylinder = 2πr,
where r is the radius of
the cylinder.
2. Breadth of
the rectangular paper = b = height (h)
of the cylinder.
3.
The curved surface area of the
cylinder is equal to the area of the rectangle = l × b = 2πr × h = 2πrh square units.
OBSERVATION
On actual measurement :
l
= ...................., b
= .....................,
2π r = l = ...................., h
= b = ....................,
Area of the rectangular paper = l × b = .................
Therefore, curved surface area of
the cylinder = 2πrh.
APPLICATION
This result can be used in
finding the material used in making cylindrical containers, i.e., powder tins,
drums, oil tanks used in industrial units, overhead water tanks, etc.
