1. 1 Creative Commons License Content Sourced and Aggregated by Centre for Positive Learning Supported by TCS iON Learning Exchange  Activity  Assess Knowledge S URFACE A REA A ND V OLUMES Class X / Term II / Math

2. A CTIVITY Topic 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. 2 Class X / Term II / Math

3. A CTIVITY 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 3 Class X / Term II / Math

4. A CTIVITY CONTD.. 4 Class X / Term II / Math

5. A CTIVITY 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] 5 Class X / Term II / Math

6. A CTIVITY 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  r =  l. θ/360  θ= 360.r/l Area of sector = Curved surface area of cone Area of sector =  l 2. θ/360 = (  l 2 /360).( 360.r/l) =  rl Curved surface area of a cone =  rl. 6 Class X / Term II / Math

7. A CTIVITY CONTD.. Conclusion The curved surface area of a cone =p (radius of base)×(slant height of the cone) 7 Class X / Term II / Math

8. A SSESS K NOWLEDGE CCE 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. 8 Class X / Term II / Math