Basic terms… Circles

By Rashmi Kathuria

Basic terms related

to circle

What is a circle?A circle is a locus of a point in a plane which

moves such that its distance from

a fixed point in the same plane remains

constant.The fixed point is

called the centre of the circle and the fixed distance is

called the radius.

O

P

Here O is the centre and OPis the radius.

The bottom and top of a bucket is usually a circle.A playing drum is circular. A clock is usually circular. The top of the table shown below is a circle.

Look around you! There are circles everywhere!

Centre & radius

Chord

Minor arc & major arc

Diameter

Minor segment & major segment

Central angle

CircumferenceCircular region

Sector

A line segment joining any two points

on the circle is called a chord of a circle.

O

Here AB is a chord .

A B

Chord

A chord passing through the centre of the circle is called the diameter . It is

the longest chord.

A B

C

D

Here AB is diameter.

Diameter

The circumference of a circle is the distance

around the outside of it.

Here light blue portion is circular region.

Circumference

A circle along with its interior is called the

circular region.

Circular region

Circular region

Any two points of the circle divide the circle into two parts called the arcs .

The smaller part is called the minor arc and the larger part is called the major

arc. In case the two parts are equal each one of them is called a semicircle. .

Horizontal lines regionis the minor segment and the remaining circular region is the major segment

Minor arc ,Major arc

A chord divides a circular region into two parts called the segments of the

circular region. The smaller segment is called as minor segment and the larger

segment is called as the major segment.

Horizontal lines regionis the minor segment and the remaining circular region is the major segment

Minor Segment,Major Segment

The angle subtended by an arc at the

centre of the circle is called the central

angle.

A

B

Central angle

A

B

Corresponding to a given arc, the region bounded by thetwo radii and the arc itself.Sector