Notes On Basic Concepts of a Circle - CBSE Class 9 Maths

There are many objects around us that are circular in shape. A circle is defined as the collection of all the points on a plane that are at equal distance from a given fixed point on the plane. This fixed point is called the centre of the circle and the fixed distance is called the radius.

A circle divides the plane on which it lies into three parts. They are (i) inside the circle, which is also called the interior of the circle; (ii) the circle and (iii) outside the circle, which is also called the exterior of the circle. The circle and its interior together form the circular region.

Circumference
The circumference of a circle is the actual length around the circle. It is the length of the edge of the circle traced around the centre of the circle.

Radius
A line segment joining the centre of a circle with any point on its circumference is called the radius of the circle.

Chord
A line that joins two points on the circumference of a circle is called a chord.

Diameter
A chord that passes through the centre of a circle is called the diameter of the circle. A diameter divides a circle into two equal segments, each is called a semicircle. Diameter is the longest chord of a circle. The diameter of a circle is twice the radius.

Arc
The part of the circumference of a circle between two given points is called an arc.The shorter arc between two given points on the circumference of a circle is called as the minor arc whereas the longer arc is called as the major arc.

Segment
A chord of a circle divides the circle into two regions called the segments of the circle. The region bounded by the chord and the minor arc intercepted by the chord is called the minor segment. The region bounded by the chord and the major arc intercepted by the chord is called the major segment.


Sector
The region between two radii of a circle and any of the arcs between them is called a sector. Sector corresponding to the minor arc is called the minor sector. Sector corresponding to the major arc is the major segment.

Summary

There are many objects around us that are circular in shape. A circle is defined as the collection of all the points on a plane that are at equal distance from a given fixed point on the plane. This fixed point is called the centre of the circle and the fixed distance is called the radius.

A circle divides the plane on which it lies into three parts. They are (i) inside the circle, which is also called the interior of the circle; (ii) the circle and (iii) outside the circle, which is also called the exterior of the circle. The circle and its interior together form the circular region.

Circumference
The circumference of a circle is the actual length around the circle. It is the length of the edge of the circle traced around the centre of the circle.

Radius
A line segment joining the centre of a circle with any point on its circumference is called the radius of the circle.

Chord
A line that joins two points on the circumference of a circle is called a chord.

Diameter
A chord that passes through the centre of a circle is called the diameter of the circle. A diameter divides a circle into two equal segments, each is called a semicircle. Diameter is the longest chord of a circle. The diameter of a circle is twice the radius.

Arc
The part of the circumference of a circle between two given points is called an arc.The shorter arc between two given points on the circumference of a circle is called as the minor arc whereas the longer arc is called as the major arc.

Segment
A chord of a circle divides the circle into two regions called the segments of the circle. The region bounded by the chord and the minor arc intercepted by the chord is called the minor segment. The region bounded by the chord and the major arc intercepted by the chord is called the major segment.


Sector
The region between two radii of a circle and any of the arcs between them is called a sector. Sector corresponding to the minor arc is called the minor sector. Sector corresponding to the major arc is the major segment.

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