Page 75 - Mathematics Class - X

Unit 6 Mensurationtion
Mensura

ACTIVITY 6.1

OBJECTIVE
To obtain formula for area of a circle experimentally.

MATERIALS REQUIRED
Thread of different colours Cardboard Adhesive
Scissors Thick sheet of paper Ruler

PRE-REQUISITE KNOWLEDGE
1. Concept of area of circle and triangle 2. Circumference of a circle

THEORY
1
1. Area of a triangle = × (base × height) sq units
2
2. Circumference: The distance around a circle is called the circumference, it is equal to 2 pr units,
where r is radius of the circle.
3. Area of a circle = pr .
2

PROCEDURE
1. Draw a circle of radius (say) r units on a thick sheet of paper.

2. Cut it out and paste it on the cardboard.
3. Cut the threads of different sizes in pairs.
4. Fill up the circle by pasting one set of threads of different sizes in concentric pattern so that there is no gap
left in between the threads as shown in Fig. (a).
5. Arrange the other set of coloured threads starting from smallest to the largest in the pattern as shown in Fig.
(b). Last thread will be of same length as that of the outermost thread of the circle as shown in Fig. (b).
6. Number and size of threads pasted on the circle and number and size of threads pasted in the form of triangle
are the same.

Fig. (a) Fig. (b)

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