Page 168 - New Medley 5 Semester 2

Circumference of a Circle

The boundary of a circle is a curved line, so it cannot be measured using
a ruler. How can it be measured?

Let us perform an activity to measure the circumference using a string and
a ruler.

Activity 1: To find the circumference of a circular object like a bangle, a
coin, a carom coin, etc., follow these steps:

1. Take a circular object, say a carom coin, and mark off a point on its
circumference.

2. Then, put one end of the string at that point and go round
the coin till you come back to the initial point.

3. Using the ruler, measure the length of the string. This gives

the circumference of the carom coin.

Relationship Between Diameter and Circumference

Let us perform another activity.

Activity 2: Follow these steps to establish the relationship between diameter
and circumference of a circle.

1. Take three carrom coins of same size and put them side-by-side as
shown in the following figure.

2. Place the string, used in Activity 1 to measure the circumference of
a coin, across the centres of coins.

What do you observe?

It is observed that the string covers all the three diameters and a little
string is left. That means, the circumference is little more than three times

the diameter of a circle.

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