1. Radius and diameter of a circle

2. Radius : The radius is a line segment with
one end point at the centre and the other
end on the circle. It is denoted by ‘r’. r O A
Diameter : Diameter is a chord passing through the centre of the circle. It is denoted by ‘d’. O A B d

3. Relationship between diameter and radius:
Diameter of a circle is twice of its radius.
Formula:
Diameter = 2 x radius
Radius = r O r A B d

4. Pi (π)
The ratio of circumference to diameter is constant for all circles. This ratio is called Pi and is written as π. Where π = C = π ⇒
C = πd ⇒
C = 2πr d 22 7

5. Example 1 : Find out the Diameter of a circle whose radius is 5 m.
Solution Given:- radius(r)= 5 To Find:- diameter(d) Diameter of a circle (d) = 2 x radius = 2 x 5 = 10m (ans)
Example 2 : Find out the Diameter of a circle whose radius is 24 m.
Solution Given:- radius(r)= 24 m To Find:- diameter(d)
Diameter of a circle (d) = 2 x radius
= 2 x 24
= 48 m (ans)

6. Example 3 : Find out the radius of a circle whose diameter is 8 m.
Solution Given:- diameter(d) = To Find:- radius(r)
Example 4 : Find out the radius of a circle whose diameter is 36 m.
Solution Given:- diameter(d) = 36 m To Find:- radius(r)

7. Try these Find out the radius of a circle whose diameter is 63 cm.
Find out the Diameter of a circle whose radius is 11 m.