Parts of a Circle with Diagrams

A circle is a curve in the plane that consists of all points that have the same distance from a fixed point, called the center. The common distance of the points from the center is called the radius. The region covered by the circle is called the area of the circle and the curve is referred to as the circumference of the circle.

Here, we will learn about the most important parts of a circle. We will look at the definitions of these parts and get to know some relevant formulas that can be used to find different lengths.

GEOMETRY
diagram of the perimeter of a circle

Relevant for

Learning about the important parts of a circle.

See parts

GEOMETRY
diagram of the perimeter of a circle

Relevant for

Learning about the important parts of a circle.

See parts

Names of the parts of a circle

A circle can have different parts based on position and shape. The most fundamental parts are the following:

  • Center
  • Radius
  • Diameter
  • Circumference
  • Tangent
  • Secant
  • Chord
  • Arc
  • Segment
  • Sector

These parts may be present depending on how the lines are drawn in the circles.


Details of the parts of a circle

Let’s look at a brief definition of the parts of a circle:

Center

The center is a fixed point on the circle, which is used to define the circle. All circles have a center and it is often represented using its Cartesian coordinates, (ab), where, a is the position on the x-axis and b is the position on the y-axis.

center of a circle

Radius

The radius of a circle is a straight line drawn from the center to the boundary of the circle or the circumference. The radius is many times represented by “R” or “r“.

radius of a circle

Diameter

The diameter is the line that crosses the circle and passes through the center. This line is twice the length of the radius. We use the letter “d” to represent the diameter. Radius and diameter are related by d=2r.

diameter of a circle

Circumference

The circumference is the length of the contour around the circle. We represent the circumference with the letter “C“. To find the circumference, we can use the formula C= \pi d or equivalently C = 2 \pi r.

circumference of a circle

Tangent

A tangent is a straight line that touches the circle at a single point. The tangent does not cut the circle. The point at which the tangent touches the circle is called the point of contact.

tangent of a circle

Secant

A secant is a line that intersects the circle at a minimum of two different points.

secant of a circle

Chord

A chord is a line segment that joins two different parts of the circumference of a circle. A chord that passes through the center of a circle is known as the diameter. This means that the diameter is the largest chord that can be drawn.

chord of a circle

Arc

An arc is a part of the circumference between two points. In the following image, the smallest arc between points P and Q is called the minor arc. The largest arc between points P and Q is called the major arc.

arc of a circle

Segment

Part of a circle bounded by a chord and an arc is known as a segment of the circle. The figure below shows the major and minor segments of a circle.

segment of a circle

Sector

A sector of a circle is the part bounded by two radii and an arc of the circle. In the following figure, AOB is a sector of a circle, where O is the center.

sector of a circle

See also

Interested in learning more about circles? Take a look at these pages:

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