Circles One centre, endless points—welcome to the perfect curve.

One Perfect Loop

Circle

A circle is all points in a plane that are the same distance from one fixed point, the centre.

Which word tells us that each point lies equally far from the centre?

Radius & Diameter

Radius & Diameter

Radius joins the centre to a point on the circle. Diameter crosses the centre, touches two opposite points, and equals \(2 \times\) radius.

Key Characteristics:

  • Both are straight line segments within a circle.
  • All radii of one circle are equal in length.
  • Diameter is the longest chord of the circle.
  • Diameter equals two radii end-to-end.

Example:

If radius = 3 cm, diameter = 6 cm.

Chord & Arc

https://asset.sparkl.ac/pb/sparkl-vector-images/img_ncert/DW7P3VitZaDkgBlgyRsjgprtQiMW9j6wqJL3o6Mn.png

Spot the Parts

Identify the straight line as the chord and the matching curved piece as the arc.

Key Points:

  • Chord: straight line joining two points on the circle.
  • Arc: curved part between the same two points.
  • Diameter is the longest chord.

Name the Parts

Drag each label onto the circle to show the centre, a radius and the diameter.

Draggable Items

Centre
Radius
Diameter

Drop Zones

Centre spot

Radius line

Diameter line

Tip:

The radius is always half the diameter.

Quick Check

Question

Which statement about a circle is true?

A
Every chord is a diameter.
B
Every diameter is a chord.
C
A radius is longer than a diameter.
D
The centre lies on the circle.

Hint:

A diameter is a special chord that passes through the centre.

Circle Snapshot

A circle is the set of points equidistant from a fixed centre.

Centre, radius, and diameter form the circle's basic framework.

A chord links two points; an arc is the curved path between them.

The diameter is the longest possible chord in a circle.

Thank You!

We hope you found this lesson informative and engaging.