Basic Definition and Terms related to Circle: Class 10th NCERT Notes

Areas Related to Circles

  • A circle is a shape consisting of all points in a plane that is a given distance from a given point, the centre; i.e it is the curve drawn out by a point that moves in a plane so that its distance from a given point is constant.

Center | Centre (Circle)

Some of real-world examples are: Cycle wheels, round cake, bangles, round pizza, Coins etc

The coin has a circular shape

Oggi's Pizza Express Bicycle, bike, biking, cycle, cycling, wheel icon


After knowing the concept of circle let’s get into some of the important Terminology of the circle:

Term Definition
Annulus a ring-shaped object, the region bounded by two concentric circles.
Arc any connected part of a circle. Specifying two endpoints of an arc and a centre allows for two arcs that together make up a full circle.
Centre the point equidistant from all points on the circle.
Chord a line segment whose endpoints lie on the circle, thus dividing a circle into two segments.
Circumference the length of one circuit along the circle, or the distance around the circle.
Diameter a line segment whose endpoints lie on the circle and that passes through the centre
Disc the region of the plane bounded by a circle.
Radius a line segment joining the centre of a circle with any single point on the circle itself
Sector a region bounded by two radii of equal length with a common center and either of the two possible arcs, determined by this center and the endpoints of the radii.
Segment a region bounded by a chord and one of the arcs connecting the chord’s endpoints. The length of the chord imposes a lower boundary on the diameter of possible arcs.
Secant an extended chord, a coplanar straight line, intersecting a circle in two points.
Semicircle one of the two possible arcs determined by the endpoints of a diameter, taking its midpoint as centre.
Tangent a coplanar straight line that has one single point in common with a circle (“touches the circle at this point”).

File:CIRCLE LINES.svg File:Circle slices.svg


CD General Computer Disc Disk Music Data IT Secondary Bw RGB Illustration

Above figures describe what exactly each terminology look like.

Now let us get into detailed concepts of each terminology of the circle starting with Perimeter and Area of a Circle.

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