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How to Draw a circle?

A circle can be drawn simply by tracing the outline of circular objects like a coin, a bangle
or a bowl, etc. To draw a circle of a given radius, we use a pencil, a compass and a ruler.

Let us draw a circle of radius 3 cm.

Step 1: Place the pointed end
of the compass at the
0 mark of the ruler.
Stretch the other arm 3 cm
of the compass to the 3

cm marking on the ruler. Centre of
the circle

Step 2: Place the pointed end of
the compass on the paper and hold the upper end firmly. Rotate the pencil

arm keeping the pointed arm fixed. Thus, a circle of radius 3 cm is formed.
relationship between the radius and the Diameter of a circle

Look at the given figure.

Clearly, the diameter of a circle is two times the radius.
Diameter
Diameter = 2 × Radius Radius Radius
O
If we know the length of the radius of a circle, we can find the length
of its diameter and vice versa.

Example: Look at the given circles and find the missing measure.
(a) A (b) H
3 cm ?

B O C E O F
? 8 cm

Solution:
(a) Radius (OA) = 3 cm (b) Radius (OH) = ?

Diameter (BC) = 2 × OA Diameter (EF) = 8 cm
= 2 × 3 cm That is, 2 × OH = 8 cm

= 6 cm So, OH = (8 ÷ 2) cm = 4 cm

Practice time 7D

1. Write true or false for the following statements.

(a) A circle is a polygon.

(b) All radii of a circle are of equal length.

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