Circumference of a circle

Circumference of a circle

In the previous section, you learnt on how to find the perimeter of a parallelogram and a trapezium. In this section, you will learn to find the circumference of a circle. Let us start with the main parts of the circle.

Figure ABCDA is known as a circle. Point O is the centre of the circle. The line AC is the diameter of the circle and OB is its radius. Also, OA and OC are the radii. Therefore, the diameter is twice the radius. However, the centre, diameter and the radius are all imaginary parts of the circle. In reality, these parts do not exist.

Find the circumference of a circle with a diameter 14 cm. Use π = 22/7.

Solution

The circumference of the circle = πd

= 22/7 × 14 cm

= 44 cm

Therefore, the circumference of the circle is 44 cm.

Example 2

Find the circumference of a circle of radius 14 cm. Use π = 22/7.

Solution

Circumference of a circle = 2πr

= 2 × 22/7 × 14 cm

= 88 cm

Therefore, the circumference of the circle is 88 cm.

Example 3

Find the circumference of a semi-circular figure with a diameter 7 cm. Use π = 22/7.

Find the circumference of a circle and divide it by two, then add its diameter.

Circumference of a semi-circular figure is πd/2

= 22/7 × 7/2 cm + 7 cm

= 18 cm

Therefore, the circumference of the semi-circular figure is 18 cm.