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Content Sourced and Aggregated by Centre for Positive Learning

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Activity Assess Knowledge

SURFACE AREA AND VOLUMES

Class X / Term II / M

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ACTIVITYTopic To find the formula for curved surface area of

a cone-using the formula for the area of sector of a circle

Objectives After performing the activity, the learner

should be able to state the formula for the curved surface area of a cone and calculate it when asked for.

Class X / Term II / M

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ACTIVITY CONTD..Pre-requisite knowledge (i) Idea of a cone

(ii) Area of sector of a circle(iii) Length of arc of sector of a circle.

Materials required : (i) Thick white sheet

(ii) Red paper(iii) Sketch pens(iv) Pair of scissors/cutter(v) Fevicol

Class X / Term II / M

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ACTIVITY CONTD..

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ACTIVITY CONTD..Steps to perform the activity (i) Take a cone made of thick red paper of

slant height l and radius r(ii) Cut the curved surface of cone along any slant height by a cutter(iii) Paste the cut-out in the form of sector of a circle, of radius l on a white sheet of paper[See figure (ii) above]

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ACTIVITY CONTD..Demonstration Let q be the central angle of circle of which

sector is a part. It can be seen that circumference of base of cone forms the arc length of the sector\ 2pr = 2pl . θ/360 θ= 360 .r/l

Area of sector = Curved surface area of cone Area of sector = pl2 . θ/360 = (pl2/360).(360 .r/l) = prl

Curved surface area of a cone =prl.

Class X / Term II / M

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ACTIVITY CONTD..Conclusion The curved surface area of a cone =p

(radius of base)×(slant height of the cone) Class X / Term II / M

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ASSESS KNOWLEDGECCE Questions (5 Marks)1. A cone of height 24cm and radius of base 6cm

is made up of modeling clay. A child reshapes it in the form of a sphere. Find the radius of the sphere.

2. A shuttle cork used for playing badminton has the shape of the combination of which basic solids?

3. What is a frustum of a right circular cone?4. Does a frustum has two circular ends with equal

radii?5. Give the formula for the volume of the frustum

of a cone.

Class X / Term II / M

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