Let’s do an activity to understand the
basics of circle
Trace a circle on a paper using any circular object such as a big bottle cap or
a bangle and cut along the traced lines.
Fold the cut circle into half. We will get semicircle. Now unfold the
semicircle and see the pleat formed is called the diameter of circle.
Again fold the half folded circle again into half. We will get a quadrant. Now
open the fold of quadrant. We will see 4 pleat meeting at a common
point. This point is called center of the circle and pleats meeting at a
point are called radii of the circle.
If we fold any part of the circle now. The pleat formed is called the chord
of the circle.
The length of the boundary formed after tracing is called the circumference
of the circle.
Circle - A circle is a
closed curve. Points on the border of the circle are equidistant from the
center of the circle.
Radius – Radius is any line
segment from center to the edge of the circle.
All radii of the circle are equidistant from the edge
of the circle i.e. all radius are equal in length.
Diameter – Diameter is a
line segment that starts at one side of circle, passes through the center of
the circle and touches the other end of the circle.
Diameter = 2 x radius
Radius = D/2
Radius = 6 cm
Diameter = 2 x 6 cm
= 12 cm
Diameter = 18 cm
Radius = 18/2
= 9 cm
All diameter of the given circle are equal in length.
Each diameter is formed of two radii. Diameter is twice the length of the
The length of the boundary of a circle is called circumference of a circle.
Chord – Line segment joining
any two points on the edge of the circle is called chord. Diameter is longest
chord of the circle.
Arc – Any part of the
circumference of the circle is called arc.