CBSE Book Class 7 Maths Activity 9

To find the ratio of circumference of a circle to its diameter.

Learning Objective : To understand that the ratio of circumference of a circle to its diameter is constant.

Pre-requisite : Concept of a circle, circumference, diameter and ratio.

Materials Required : A ruler, thick paper like drawing sheet, three different sized bottle cans having circular base/three bangles of different sizes, a pair of scissors, a sketch pen.

Procedure :

Step 1. Draw three circles using three different sized bottle cans or bangles on a thick paper [Fig. 9(a)]. Mark them as circle, 1, 2 and 3

Step 2. Cut out all the three circular discs with the help of pair of scissors.

Step 3. Mark the diameter of each circle by folding each circle in two halves. [Fig. 9(b)]. Name these diameters as AB, CD and EF respectively.

Step 4. Draw a ray on a paper and mark its nitial point as G. [Fig. 9(c)]

Step 5. Hold one of the cirles, say, circle 3 in upright position on a paper such that the point E on the circle coincides with the point G on the ray [Fig. 9(d)]

Step 6. Rotate the circle along the ray and keep on rotating until the point E again touches the ray. Mark that point on line as H [Fig. 9 (e and f)]

Step 7. Measure the distance GH with the help of a ruler.

Step 8. Measure the diameter EF with the help of a ruler.

Record these measurements on a paper.

Step 9. Repeat the above Steps for circles 2 and 1.

Please refer to the link below - CBSE Class 7 Maths Activity 9